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

> Attacker can write files outside cache directory via malicious conda channel metadata, potentially leading to code execution.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 9 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** GHSA-h672-p7h7-97v9, PYSEC-2026-2970

## What is CVE-2026-53956?

CVE-2026-53956 is a medium-severity path traversal vulnerability in conda py-rattler, published on 9 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-73 (External Control of File Name or Path), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-53956?

5 open source packages ship an affected version, including py-rattler, py_rattler and rattler_cache.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `py-rattler` | PyPI | All versions | 0.24.0 |
| `py-rattler` | PyPI | All versions | 0.24.0 |
| `py_rattler` | PyPI | All versions | 0.24.0 |
| `rattler_cache` | crates.io | All versions | 0.9.0 |
| `rattler_cache` | crates.io | All versions | 0.9.0 |

## How do I fix CVE-2026-53956?

Upgrade py-rattler to 0.24.0 or later.

## Is CVE-2026-53956 being exploited?

There is no known exploitation of CVE-2026-53956 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53956 and fix it if it is affected.

What it is: CVE-2026-53956 is a medium-severity path traversal vulnerability in conda py-rattler, published on 9 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-53956 in the wild and no public exploit code.

Affected packages and fixed versions:
- py-rattler (PyPI): affected all versions; fixed in 0.24.0
- py-rattler (PyPI): affected all versions; fixed in 0.24.0
- py_rattler (PyPI): affected all versions; fixed in 0.24.0
- rattler_cache (crates.io): affected all versions; fixed in 0.9.0
- rattler_cache (crates.io): affected all versions; fixed in 0.9.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-53956/ (Markdown: https://insights.sbomify.com/CVE-2026-53956/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53956
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53956
- OSV: https://osv.dev/vulnerability/CVE-2026-53956

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53956/
Summaries are generated and may contain mistakes; the official description above is the record.