CVE-2026-33747 is a path traversal flaw in BuildKit, the build engine behind Docker builds. NVD scores it 8.4. A custom frontend can craft an API message that writes files outside the BuildKit state directory. Upgrade to BuildKit 0.28.1. Well known frontends such as docker/dockerfile are not affected, per the advisory.
What's affected
BuildKit versions before 0.28.1 are affected, and 0.28.1 fixes it, per the advisory and release notes. The issue requires an untrusted custom frontend, set with a #syntax line or the BUILDKIT_SYNTAX build argument. The advisory says well known frontend images such as docker/dockerfile are not affected.
How to check if you're exposed
docker buildx version
docker buildx inspect --bootstrap
The inspect output shows the BuildKit version of your builder. Then search your repositories and CI configuration for custom syntax references:
grep -rn "syntax=" --include=Dockerfile* .
grep -rn "BUILDKIT_SYNTAX" .
Any frontend image you do not control or pin to a trusted digest is the risk, particularly in CI that builds code from outside contributors.
What to do now
- Upgrade BuildKit to 0.28.1 or later, including builders embedded in Docker Engine and CI runners.
- Allow only well known frontends, and remove untrusted
#syntaxlines. - Build untrusted code on disposable, isolated builders without access to credentials.
- Add builder versions to your inventory.
Why it matters
The record uses CWE-22, path traversal. A frontend is code that runs as part of the build, and the engine failed to confine the paths it asked to write. Build systems run with access to caches, tokens and registries, so a write outside the sandbox boundary matters. The record is not marked as exploited in the wild and is not in CISA KEV.
Treat a build frontend like any other code you execute. Pin frontends by digest where you use them, and keep untrusted builds away from machines that hold registry credentials. If your CI builds pull requests from forks, run those builds on short lived builders with no secrets.
Try it yourself
Click through it at your own pace, or open it full screen.
Quick check
Am I affected using docker/dockerfile?
The advisory says well known frontend images like that are not affected.
Sources
Last reviewed: 19 October 2026.
