Vulnerability · Published Nov 3, 2026 · Assigned by Docker
CVE-2026-121520Malicious client could set xattr value outside of BuildKit state directory
Medium 4.5
In plain English
A medium-severity security flaw in BuildKit from Moby. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 3% of all known vulnerabilities).
Official description
In BuildKit versions prior to v0.34.1, a malicious client with access to the BuildKit control APIs can submit a build request that sets an extended attribute on a file outside the BuildKit state directory. Extended attributes in the trusted. or security. namespaces may also be set, potentially giving a program on the host elevated privileges. This issue affects build services that accept build requests from untrusted users. The issue is fixed in v0.34.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:26.04:LTS | docker.io | no fix listed | UBUNTU-CVE-2026-121520 |
| Ubuntu:26.10 | docker.io | no fix listed | UBUNTU-CVE-2026-121520 |
| Ubuntu:26.04:LTS | docker.io-app | no fix listed | UBUNTU-CVE-2026-121520 |
| Ubuntu:26.10 | docker.io-app | no fix listed | UBUNTU-CVE-2026-121520 |
Affected products (as reported)
Weakness: CWE-61 · Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:H