CVE-2025-32799 is a critical (CVSS 9.8) path traversal flaw, often called Tarslip, in conda-build before version 25.4.0. Tar entries with directory traversal names can write files outside the intended extraction folder. The fix is conda-build 25.4.0. Upgrade, and avoid unpacking archives you do not trust.
What's affected
conda-build versions before 25.4.0, per the CVE record. The advisory says the issue was patched in 25.4.0.
The record says the processing logic does not properly sanitize the paths of tar entries. A crafted archive can therefore contain entries that climb out of the extraction directory. The record lists arbitrary file overwrites, privilege escalation and code execution as possible results when sensitive locations are targeted.
The code paths the advisory points to are in the package conversion and recipe rendering modules, which handle archives during normal work.
How to check if you're exposed
Check the version in every environment or image that has conda-build:
conda list conda-build
If you installed it with pip:
pip show conda-build
Anything below 25.4.0 needs the update. Also list where you run conversion or rendering on archives from third parties, because those are the workflows the weakness touches.
What to do now
- Upgrade to conda-build 25.4.0 or later everywhere it is installed.
- Do not convert or render archives from unknown sources with the old version.
- Run builds under an account that cannot write outside its workspace.
- Use disposable build environments so any stray file write is discarded with the environment.
- Check build hosts for unexpected changes in shell profiles, cron entries and tool configuration if untrusted archives were processed.
Why it matters
The class is CWE-22 (Path Traversal). Archive entries carry their own names, and a name can include steps that move up a directory. Extraction code has to check that each final path stays inside the destination. Without that check, the archive decides where its files land.
Because the build account often has write access to places such as home directories and caches, an overwrite can be turned into code execution on the next run. This sits alongside CVE-2025-32798, the eval issue, and CVE-2025-32800, the unregistered dependency, in the same release line.
A useful habit is to treat every archive as hostile until extraction has been checked. Libraries for tar and zip handling in several languages now offer filters that reject absolute paths and parent directory steps. When you write extraction code, use those filters, or resolve each final path and confirm it is inside the target folder before writing a single byte.
The record does not mark this CVE as CISA KEV and makes no claim of exploitation in the wild.
Quick check
Is this only about conda packages?
The record describes tar entries handled by conda-build in general. Treat any tar archive processed by the old version from an untrusted source as a risk.
Sources
Last reviewed: 18 October 2026.
