CVE-2026-53956 Overview
CVE-2026-53956 is a path traversal vulnerability [CWE-22] in Rattler, a library providing common functionality within the conda ecosystem. The flaw affects rattler_cache prior to version 0.9.0 and py-rattler prior to version 0.24.0. During cache materialization, the code uses the package record build string as part of a cache key joined into a filesystem path. A malicious conda channel can publish repodata containing path separators or traversal components in that field, causing package contents to be written outside the configured package cache directory.
Critical Impact
An untrusted conda channel can write files outside the intended cache directory, potentially overwriting sensitive files on the host filesystem.
Affected Products
- rattler_cache versions prior to 0.9.0
- py-rattler versions prior to 0.24.0
- Applications consuming untrusted conda channels via Rattler
Discovery Timeline
- 2026-09-09 - CVE-2026-53956 published to NVD
- 2026-09-09 - Last updated in NVD database
Technical Details for CVE-2026-53956
Vulnerability Analysis
Rattler processes conda channel repodata to materialize packages into a local cache directory. The caching layer constructs a per-package cache key that incorporates the build string field from the package record. This key is joined onto the configured cache root using standard path-join semantics.
The implementation does not sanitize or validate the build string before treating it as a path component. When a package record contains characters such as /, \, or .. in the build field, the resulting path escapes the intended cache directory. Package contents extracted during cache materialization then land at attacker-chosen locations on the host filesystem.
Exploitation requires the victim to use a malicious or untrusted conda channel. Curated channels that validate package metadata are not expected to permit malformed build strings.
Root Cause
The root cause is improper limitation of a pathname to a restricted directory [CWE-22]. The rattler_cache code trusts channel-supplied metadata as a safe path component without applying allowlist validation, canonicalization, or a containment check against the cache root.
Attack Vector
An attacker publishes or controls a conda channel that serves crafted repodata. The malicious repodata contains a package record whose build field embeds traversal sequences or absolute path fragments. When a Rattler-based client fetches and materializes the package, the extracted files are written outside the cache directory, enabling arbitrary file write within the running process's privileges. See the GitHub Security Advisory GHSA-h672-p7h7-97v9 for further technical detail.
Detection Methods for CVE-2026-53956
Indicators of Compromise
- Files created outside the configured conda package cache directory during or after package install operations
- Conda channel repodata containing build string values with /, \, or .. sequences
- Unexpected modifications to configuration files, shell profiles, or scheduled task directories following a Rattler-driven install
Detection Strategies
- Audit repodata fetched from any non-curated conda channels for malformed build fields prior to processing
- Monitor filesystem write activity from Python or Rust processes hosting py-rattler or rattler_cache and alert on writes outside the cache root
- Inventory installed versions of rattler_cache and py-rattler across build servers and developer endpoints
Monitoring Recommendations
- Enable file integrity monitoring on directories adjacent to and above configured conda cache paths
- Log all conda channel URLs configured across CI/CD pipelines and developer workstations
- Alert on process execution of package managers that reference channels outside an approved allowlist
How to Mitigate CVE-2026-53956
Immediate Actions Required
- Upgrade rattler_cache to version 0.9.0 or later
- Upgrade py-rattler to version 0.24.0 or later
- Restrict conda channel configuration to curated, trusted sources only
- Review recent package installations sourced from untrusted channels for signs of files written outside the cache directory
Patch Information
The conda project addressed the issue in rattler_cache 0.9.0 and py-rattler 0.24.0. The fix validates the build string before it is incorporated into a filesystem path, preventing traversal outside the cache root. Details are available in the GitHub Security Advisory GHSA-h672-p7h7-97v9.
Workarounds
- Configure Rattler to consume only vetted internal channels or well-known curated channels such as conda-forge and defaults
- Pre-validate any third-party repodata for malformed build strings before allowing package materialization
- Run Rattler-based tooling under a least-privileged account that cannot write to sensitive filesystem locations
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
