# CVE-2026-82331: Apache BuildStream: tar source extraction escape

> Malicious tarballs can write files to the host via symlink escapes during source fetching, potentially leading to code execution or data modification.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-82331, GHSA-5xjv-h9hc-3vv9, UBUNTU-CVE-2026-82331

## What is CVE-2026-82331?

CVE-2026-82331 is a critical path traversal vulnerability in Apache BuildStream, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Improper link resolution before file access ('link following') vulnerability in the `tar` source plugin of Apache BuildStream running on Python < 3.12 allows malicious source tarballs to write files on the host, with the privileges of the user running BuildStream, via symlinks as part of source fetching.
The impact of this issue is mitigated by:

* BuildStream projects should only use trusted sources in their elements as otherwise the build output can also not be trusted
* Tracking a source tarball pins its SHA256 hash, which prevents MITM attacks of users that are fetching an already tracked project
* When running on Python >= 3.12, BuildStream >= 2.3.0 already makes use of the Python `tarfile` filter functionality, which blocks the symlink escape

Users are recommended to upgrade to version 2.8.1, which fixes this issue.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2026-82331?


## How do I fix CVE-2026-82331?

Upgrade to a fixed version.

## Is CVE-2026-82331 being exploited?

There is no known exploitation of CVE-2026-82331 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82331 and fix it if it is affected.

What it is: CVE-2026-82331 is a critical path traversal vulnerability in Apache BuildStream, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-82331 in the wild and no public exploit code.

Affected product: Apache BuildStream. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-82331/ (Markdown: https://insights.sbomify.com/CVE-2026-82331/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82331
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82331
- OSV: https://osv.dev/vulnerability/CVE-2026-82331

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82331/
Summaries are generated and may contain mistakes; the official description above is the record.