PYSEC-2026-2440

### Impact _What kind of vulnerability is it? Who is impacted?_

A path traversal vulnerability exists in dbt-common's `safe_extract()` function used when extracting tarball archives. The function uses `os.path.commonprefix()` to validate that extracted files remain within the intended destination directory. However, `commonprefix()` compares paths character-by-character rather than by path components, allowing a malicious tarball to write files to sibling directories with matching name prefixes.

For example, when extracting to `/tmp/packages`, a crafted tarball could write files to `/tmp/packagesevil/` by exploiting the character-based prefix matching.

This vulnerability affects users who: - Install dbt packages from untrusted sources - Process tarball archives through dbt-common's extraction utilities

The practical risk is limited because: - Exploitation requires a malicious tarball to be processed - File writes are restricted to sibling directories with matching prefixes (not arbitrary paths) - Packages from trusted sources (dbt Hub) are not affected

This is similar to CVE-2026-1703 in pip, which had a CVSS score of 3.9 (Low).

### Patches _Has the problem been patched? What versions should users upgrade to?_

Fixed in `dbt-common` version 1.37.3 & 1.34.2, and patched for dbt-core 1.11.7 and 1.10.20 releases.

The fix replaces `os.path.commonprefix()` with `os.path.commonpath()`, which correctly compares paths by their components rather than characters.

### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_

- Only install dbt packages from trusted sources (official dbt Hub, verified git repositories) - Avoid installing packages from untrusted URLs or unverified third parties - Review package contents before installation when sourcing from external locations

### Resources _Are there any links users can visit to find out more?_

1. CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'): https://cwe.mitre.org/data/definitions/22.html 2. CVE-2026-1703 (similar vulnerability in pip): https://nvd.nist.gov/vuln/detail/CVE-2026-1703 3. pip fix PR #13777: https://github.com/pypa/pip/pull/13777 4. Python documentation on `commonpath` vs `commonprefix`: https://docs.python.org/3/library/os.path.html#os.path.commonpath