Unintended Proxy or Intermediary ('Confused Deputy') Affecting github.com/moby/buildkit/cache/util package, versions <0.33.1

Affected versions of this package are vulnerable to Unintended Proxy or Intermediary ('Confused Deputy') via the ReadFile, openUserFile, readRegularFile, and BuildOp.Exec paths in cache/util/fsutil.go, executor/oci/user.go, exporter/attestation/*.go, and solver/llbsolver/ops/*.go. An attacker can make the daemon open a FIFO, device node, socket, or symlink by placing that inode in a build snapshot and causing BuildKit to read it as if it were a regular file. This lets a build block daemon operations indefinitely on special files such as FIFOs, and on rootful workers it can make the daemon access host device nodes that the sandbox itself cannot open. The result is a denial of service for builds and, in privileged deployments, unintended host device access.

Workarounds

• Avoid untrusted builds; only run BuildKit on builds from trusted sources, so attacker-controlled snapshot contents cannot be used to trigger special-file opens or daemon hangs.
• Use rootless mode to reduce impact from special files: it mitigates unintended host device access, though it does not prevent denial-of-service from FIFOs or other blocking special files.

• GitHub Commit v0.33.1
• Maintainer's Advisory