Python: Add modelling for zstd.compression
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See https://docs.python.org/3/library/compression.zstd.html for information about this library. As far as I can tell, the `zstd` library is not vulnerable to things like ZipSlip, but it _could_ be vulnerable to a decompression bomb attack, so I extended those models accordingly.
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Pull request overview
This PR adds modeling support for Python 3.14's new compression.zstd library to detect potential decompression bomb vulnerabilities. The implementation follows the established pattern used for other compression libraries like gzip, bz2, and lzma.
- Extends the decompression bomb detection to include
zstd.open()andzstd.ZstdFile()calls when used in read mode - Adds test cases to verify the new detection capability
- Updates auto-generated expected test results
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| python/ql/test/experimental/query-tests/Security/CWE-409/test.py | Adds test cases for zstd.open() and zstd.ZstdFile() decompression bomb vulnerabilities |
| python/ql/test/experimental/query-tests/Security/CWE-409/DecompressionBombs.expected | Updates auto-generated expected test results with new test case line numbers |
| python/ql/src/experimental/semmle/python/security/DecompressionBomb.qll | Implements the Zstd module with decompression sink detection logic for Python 3.14+ |
| python/ql/lib/change-notes/2025-12-09-add-modelling-of-zstd-compression.md | Documents the addition of compression.zstd library support |
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See https://docs.python.org/3/library/compression.zstd.html for information about this library.
As far as I can tell, the
zstdlibrary is not vulnerable to things like ZipSlip, but it could be vulnerable to a decompression bomb attack, so I extended those models accordingly.