BuildKit: Xattr Abuse Prior to v0.34.1
CVE-2026-121520 Published on November 3, 2026
Malicious client could set xattr value outside of BuildKit state directory
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.
Weakness Type
What is a Symlink following Vulnerability?
The software, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the software to operate on unauthorized files. A software system that allows UNIX symbolic links (symlink) as part of paths whether in internal code or through user input can allow an attacker to spoof the symbolic link and traverse the file system to unintended locations or access arbitrary files. The symbolic link can permit an attacker to read/write/corrupt a file that they originally did not have permissions to access.
CVE-2026-121520 has been classified to as a Symlink following vulnerability or weakness.
Affected Versions
Moby BuildKit:- Before 0.34.1 is affected.