Rattler is a library used within the conda ecosystem. Versions of rattler_cache before 0.9.0 and py-rattler before 0.24.0 are vulnerable to a package-cache path traversal vulnerability (CVE-2026-53956). The vulnerability arises because the package record's build string is used as part of a cache key that is joined into a filesystem path without proper sanitization. A malicious conda channel could publish repodata with path separators or traversal sequences in the build string, causing files to be written outside the configured package cache directory. This can lead to integrity issues with the package cache. The issue requires a malicious or untrusted channel; curated channels that validate package metadata are not expected to allow such malformed build strings.

The vulnerability allows an attacker controlling or influencing a conda channel to cause package contents to be written outside the intended package cache directory via path traversal in the build string. This could lead to integrity issues or potential denial of service by overwriting files outside the cache. There is no indication of confidentiality or direct code execution impact. The attack requires user interaction with a malicious or untrusted channel.

A patch is available. Users should upgrade to rattler_cache version 0.9.0 or later and py-rattler version 0.24.0 or later. Additionally, users should avoid using untrusted or malicious conda channels, as curated channels that validate package metadata are not expected to allow malformed build strings. No other mitigation is indicated.