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vuln-fix: Zip Slip Vulnerability
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This fixes a Zip-Slip vulnerability.

This change does one of two things. This change either

1. Inserts a guard to protect against Zip Slip.
OR
2. Replaces `dir.getCanonicalPath().startsWith(parent.getCanonicalPath())`, which is vulnerable to partial path traversal attacks, with the more secure `dir.getCanonicalFile().toPath().startsWith(parent.getCanonicalFile().toPath())`.

For number 2, consider `"/usr/outnot".startsWith("/usr/out")`.
The check is bypassed although `/outnot` is not under the `/out` directory.
It's important to understand that the terminating slash may be removed when using various `String` representations of the `File` object.
For example, on Linux, `println(new File("/var"))` will print `/var`, but `println(new File("/var", "/")` will print `/var/`;
however, `println(new File("/var", "/").getCanonicalPath())` will print `/var`.

Weakness: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Severity: High
CVSSS: 7.4
Detection: CodeQL (https://codeql.github.com/codeql-query-help/java/java-zipslip/) & OpenRewrite (https://public.moderne.io/recipes/org.openrewrite.java.security.ZipSlip)

Reported-by: Jonathan Leitschuh <[email protected]>
Signed-off-by: Jonathan Leitschuh <[email protected]>

Bug-tracker: JLLeitschuh/security-research#16

Co-authored-by: Moderne <[email protected]>
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JLLeitschuh and TeamModerne committed Sep 23, 2022
1 parent f75bbfd commit 52d85f1
Showing 1 changed file with 3 additions and 0 deletions.
3 changes: 3 additions & 0 deletions src/main/java/ch/digitalfondue/stampo/command/New.java
Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,9 @@ public void run() {

private void extractFile(Path outputPath, ZipEntry ze, InputStream zip) {
Path destinationPath = outputPath.resolve(ze.getName());
if (!destinationPath.normalize().startsWith(outputPath.normalize())) {
throw new RuntimeException("Bad zip entry");
}
try {
Files.createDirectories(destinationPath.getParent());
Files.copy(zip, destinationPath);
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