Moby BuildKit EUVD-2026-46309

Exploitation requires local access to the host running the BuildKit daemon (AV:L) and valid permissions to issue requests to the BuildKit control API (PR:L), such as membership in the group authorized to access the buildkitd socket or possession of a valid mTLS client certificate. The description explicitly states the client must be able to 'bypass authentication' or otherwise hold legitimate API access to issue builds. Exploitation is constrained to: (1) authenticated or authorized BuildKit API clients only - anonymous network attackers cannot exploit this; (2) local or socket-adjacent access - remote exploitation requires prior compromise of a build-authorized identity; (3) all tracked moby/buildkit versions per CPE wildcard, but only on systems where buildkitd is running and accessible.

The CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H) signals a locally exploitable flaw requiring low-privilege API access with no complexity or user-interaction barriers once access is established - resulting in a 6.9 Medium score. The local attack vector (AV:L) substantially limits the threat compared to a network-reachable vulnerability: an attacker must already operate on the same host or have network-level reach to the BuildKit socket. The PR:L requirement means the attacker must hold valid BuildKit control API credentials or permissions, ruling out fully anonymous exploitation. No EPSS score was supplied, no CVE is listed in CISA KEV, and no public proof-of-concept has been identified, making this a credible but not currently weaponized risk. The high integrity (VI:H) and availability (VA:H) impacts are meaningful in CI/CD contexts where arbitrary file writes on a build host could plant malicious artifacts or destabilize the build agent. There is no confidentiality impact (VC:N), which limits the direct data-exfiltration risk.

An attacker with legitimate access to the BuildKit control API - such as a compromised CI/CD pipeline runner or a malicious contributor with build-trigger permissions - crafts an upload request embedding path traversal sequences in the file destination path. BuildKit processes the request without stripping traversal components, writing attacker-controlled content to an arbitrary location on the host filesystem beyond the state directory. This could be used to overwrite startup scripts, inject payloads into shared library paths, or corrupt other build artifacts on a shared build host.