CVE-2026-121520

Medium

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.

SeverityMedium

CVSS4.5

Exploit probability—

ProductBuildKit

PublishedNov 3, 2026

First seenNov 4, 2026

Weakness typeCWE-61CWE-61

How to fix

Update

Moby BuildKit0.34.1 or later

Vendor advisories

github.com/moby/buildkit/security/advisories/GHSA-w26x-xg27-7qjc

Affected products

Product	Affected versions	Fixed in
Moby BuildKit	v < 0.34.1	0.34.1

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