unzip: block zip-slip via sibling-prefix paths

[staticpayload]

Context\nThe unzip path guard used a prefix check on resolved paths. A sibling path that shares the prefix (e.g. /tmp/dir vs /tmp/dir-evil) can pass the check and escape the intended output directory.\n\n## Change\nUse path.relative-based containment checks and add a regression fixture for the sibling-prefix traversal case.\n\n## Testing\n- Ubuntu 22.04 (AWS eu-west-2), Node 20\n- npx mocha --no-config --require ts-node/register --require source-map-support/register --require src/test/helpers/mocha-bootstrap.ts --file src/test/helpers/global-mock-auth.ts src/unzip.spec.ts

[gemini-code-assist]

Summary of Changes

Hello @staticpayload, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on bolstering the security of the unzip utility by implementing a more robust defense against zip-slip vulnerabilities. The core change involves refining the path validation mechanism to prevent malicious archives from extracting files outside the intended destination directory, specifically addressing sophisticated prefix-based path escapes. A new regression test case has been added to confirm the effectiveness of these enhanced security measures.

Highlights

• Enhanced Zip-Slip Protection: The path validation logic within the isChildDir function has been significantly hardened to prevent prefix-based path escapes. This refactoring utilizes path.relative to ensure that extracted files remain strictly within the designated output directory, thereby mitigating zip-slip vulnerabilities more effectively.
• New Regression Test Case: A new test fixture, zip-slip-prefix, has been introduced to specifically target and validate the improved protection against sibling-path traversal attacks. This ensures that the updated security measures are robust and cover previously exploitable scenarios.

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[gemini-code-assist]

Code Review

This pull request provides a critical security fix for a zip slip vulnerability. The previous path validation using startsWith was susceptible to prefix-based path traversal attacks. The new implementation of isChildDir correctly uses path.relative to ensure that extracted file paths are strictly within the target directory, which is a much more robust approach. The removal of the unnecessary try...catch block is also a good cleanup. Additionally, adding a regression test case for the "zip-slip-prefix" scenario is excellent practice. The changes are well-implemented and effectively address the vulnerability.