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9.8
CVE-2026-82331: Apache BuildStream tar plugin can write files via symlink
CVE-2026-82331 · published 2 days ago
Summary
If you use Apache BuildStream (including the Debian and Canonical packages) with Python older than version 3.12, a crafted source archive can cause the program to create or overwrite files on the machine where it runs. This happens because the program follows symbolic links inside the archive before checking where the files will be written. Upgrade BuildStream to version 2.8.1 (or later) to stop this behavior, and use trusted source archives with verified checksums.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| – | apache software foundation | apache buildstream | <= 2.8.0 |
| Debian:12 | debian | buildstream | All versions |
| Ubuntu:20.04:LTS | canonical | buildstream | All versions |
Original advisory text
DEBIAN-CVE-2026-82331
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.
References
- https://lists.apache.org/thread/9b342631x7bvtyg0pq7zgywtl2cmy34v Third Party Advisory
- http://www.openwall.com/lists/oss-security/2026/09/23/9
- https://security-tracker.debian.org/tracker/CVE-2026-82331 Vendor Advisory
- https://ubuntu.com/security/CVE-2026-82331 Third Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2026-82331 Third Party Advisory
Severity
9.8
Critical
Exploitation
EPSS <1%
Type
CWE-59Link Following
Timeline
Published23 Sep 2026
Updated25 Sep 2026
First seen23 Sep 2026
Sources
CVE-2026-82331 · NVD
CVE-2026-82331 · MITRE
DEBIAN-CVE-2026-82331 · OSV
UBUNTU-CVE-2026-82331 · OSV
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