CVE-2025-4517

What it actually does

The vulnerability permits writing files to arbitrary locations outside the intended extraction directory when using TarFile.extractall() or extract() with filter='data' or 'tar' on untrusted tar archives.

Why it matters to the business

Attackers could overwrite critical system or application files, potentially leading to system compromise, data loss, or unauthorized code execution in environments processing untrusted tar archives; high prevalence of Python increases exposure across many systems.

How an attack unfolds

An attacker creates a tar archive containing files with paths that traverse outside the extraction directory. When a vulnerable Python application extracts this archive using the specified filters, the files are written to unintended locations on the filesystem.

How to fix it

Update to a version of CPython that includes commit 19de092debb3d7e832e5672cc2f7b788d35951da or later. Avoid using the 'data' or 'tar' filters with untrusted archives; prefer safer filters or manual validation.

How to confirm the fix worked

Verify the Python version or source includes the fix commit. Test extraction of sample malicious tar archives to confirm files are not written outside the directory.

Typical attack path

1. Craft malicious tar archive with path traversal entries
2. Deliver archive to target application
3. Trigger extraction using TarFile.extractall() or extract() with filter='data' or 'tar'
4. Achieve arbitrary file writes

How to detect it

Review application logs for tarfile extraction operations on untrusted inputs. Look for file system changes outside expected directories during extraction processes. Audit code paths handling tar archives.

What your security team should do

• Prioritize updating Python environments to the patched commit
• Review code using tarfile extraction for use of vulnerable filters
• Implement input validation or sandboxing for tar extraction
• Monitor for unexpected file writes during archive processing