CVE-2025-4330

What it actually does

The tarfile module's extraction filters 'data' and 'tar' can be bypassed, permitting symlinks to escape the destination directory and allowing modification of certain file metadata during extraction of untrusted archives.

Why it matters to the business

Organizations using Python to unpack untrusted tar archives face risk of files being written outside intended directories and metadata tampering, potentially leading to unauthorized data placement or overwrites in automated processing pipelines.

How an attack unfolds

An attacker crafts a malicious tar archive containing symlinks pointing outside the target directory. When a victim application uses TarFile.extractall() or extract() with filter='data' or 'tar', the filter is ignored, allowing the symlink targets and metadata changes to be applied, resulting in files being placed in arbitrary locations.

How to fix it

Update Python to a build containing commit 19de092debb3d7e832e5672cc2f7b788d35951da or later. Avoid using filter='data' or 'tar' with untrusted archives until patched; prefer the stricter 'fully_trusted' filter only for trusted content or implement custom validation before extraction.

How to confirm the fix worked

Confirm the installed Python version or source includes commit 19de092debb3d7e832e5672cc2f7b788d35951da. Test extraction of a crafted tar with external symlinks using the affected filters and verify that links are rejected or confined to the destination.

Typical attack path

1. Craft a tar archive with symlinks targeting paths outside the intended extraction root and desired metadata alterations.
2. Deliver the archive to a system or service that processes it via Python's tarfile module using extractall() or extract() with filter set to 'data' or 'tar'.
3. Trigger extraction, bypassing the intended safety filter and causing files or links to be created or modified outside the destination directory.

How to detect it

Review application logs for tarfile extraction calls on untrusted archives. Look for post-extraction file system anomalies such as unexpected symlinks or files appearing outside designated directories. Examine process execution involving python and tarfile module usage around archive handling timestamps.

What your security team should do

• Prioritize patching all Python installations to the fixed commit in environments that extract untrusted tar archives.
• Audit code and dependencies for use of TarFile.extractall() or extract() with filter='data' or 'tar' on untrusted input.
• Implement pre-extraction validation or sandboxing for tar processing until upgrades are complete.
• Monitor for any new EPSS increases or exploit releases given the path traversal nature.