CVE-2026-53956: Rattler vulnerable to package cache path traversal via conda package build string

Vulnerability summary

CVE-2026-53956 is a medium (CVSS 5.4) Path Traversal vulnerability in conda py-rattler. EPSS estimates a 0.33% chance of exploitation in the next 30 days, higher than 24.8% of scored vulnerabilities.

Timeline

1. 09-09-2026
   PublishedVulnerability first disclosed.
2. 10-09-2026
   Last modifiedVulnerability information updated.

Description

Rattler is a library that provides common functionality used within the conda ecosystem. `rattler_cache` prior to version 0.9.0 and `py-rattler` prior to version 0.24.0 were vulnerable to package-cache path traversal when handling package metadata from conda channels. During cache materialization, the `ratter_cache` code used the package record `build` string as part of a cache key that was joined into a filesystem path. A malicious or untrusted channel could publish repodata with path separators or traversal components in that field, causing package contents to be written outside the configured package cache directory. The issue requires use of a malicious or otherwise untrusted conda channel. Curated channels that validate package metadata are not expected to allow malformed build strings of this form. Users should upgrade to `rattler_cache` version 0.9.0 or `py-rattler` version 0.24.0 and avoid untrusted conda channels.

• CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
• CWE-73External Control of File Name or PathThe product allows user input to control or influence paths or file names that are used in filesystem operations.