BuildKit vulnerable to possible race condition with accessing subpaths from cache mounts

Impact

Two malicious build steps running in parallel sharing the same cache mounts with subpaths could cause a race condition that can lead to files from the host system being accessible to the build container.

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 cache mounts with --mount=type=cache,source=... options.

References

https://www.openwall.com/lists/oss-security/2019/05/28/1