Docker Sandboxes 0.28.0 through 0.41.9 on macOS contained a critical escape: the virtio-fs host server followed symlinks when reopening unlinked files, letting guest code read and modify arbitrary host files as the VMM user. A guest could store a path, replace its parent directory with a symlink, and exploit this TOCTOU window to reach any file on the host. The CVE-2026-77179 vulnerability scores 9.4 CVSS.
Docker patched it in 0.42.0 (September 7) with no reported exploitation. The incident reveals a recurring gap: container escapes don’t require kernel breaks. File-sharing layers are harder to secure than most assume, especially symlink handling. Symlink resolution slips past review and testing because the attack is subtle. A race condition on parent path resolution is harder to catch than straightforward access checks. Audit symlink code in container runtimes first.
Sources: Docker Sandboxes 0.42.0 Security Update: CVE-2026-77179 and CVE-2026-79994
Coverage: Critical Docker Sandboxes Flaw Lets Malicious Guest Code Read and Modify macOS Host Files
Related on this blog: [AUTO] Sandbox Escapes, Vendor Framing • [AUTO] BragJack: One Malicious Extension, Five Browsers • [AUTO] MLflow SSRF: validating before connecting