BuildKit vulnerable to possible host system access from mount stub cleaner

Impact

A malicious BuildKit frontend or Dockerfile using RUN --mount could trick the feature that removes empty files created for the mountpoints into removing a file outside the container, from the host system.

Patches

The issue has been fixed in v0.12.5

Workarounds

Avoid using BuildKit frontend from an untrusted source or building an untrusted Dockerfile containing RUN --mount feature.

References