GHSA-4qqr-vv2q-cmr5 Crawl4AI: SSRF filter bypass in Docker server via IPv6 transition forms (NAT64 / 6to4 / unspecified / v4-mapped)

• PyPI crawl4ai: < 0.8.8 → fixed in 0.8.8

Summary The Docker API server's SSRF protection (`validate_webhook_url` / `validate_url_destination` in `deploy/docker/utils.py`) used an explicit IPv4/IPv6 CIDR blocklist that missed several address families. An attacker could reach internal services and cloud metadata endpoints (e.g. `169.254.169.254`) despite the filter by encoding an internal IPv4 address inside an IPv6 transition form, or by using the IPv6 unspecified address. Because the Docker API is unauthenticated by default (`jwt_enabled: false`), no credentials are required. Affected paths The blocklist was applied to crawl URLs (`POST /crawl`, `/md`, `/html`, `/screenshot`, `/pdf`, `/execute_js`) and webhook URLs (`/crawl/job`, `/llm/job`). All shared the same incomplete check. Bypasses The following all resolve to (or route to) blocked internal addresses but were NOT caught: • IPv6 unspecified `::` • NAT64 `64:ff9b::a9fe:a9fe` (embeds `169.254.169.254`) • 6to4 `2002:a9fe:a9fe::` (embeds `169.254.169.254`) • IPv4-mapped `::ffff:169.254.169.254` • IPv4-compatible `::a9fe:a9fe` The error message also echoed the resolved internal IP, acting as a minor DNS/oracle leak. Impact Server-Side Request Forgery: an unauthenticated attacker can make the server fetch internal-network URLs and cloud instance-metadata endpoints, potentially exposing internal services and cloud credentials. Fix The blocklist is replaced by a single rule: reject any resolved IP where `not ip.is_global`, evaluated on the address AND every embedded IPv4 transition form (v4-mapped, NAT64 `64:ff9b::/96`, 6to4 `2002::/16`, v4-compat `::/96`). Error messages are now opaque and no longer echo the resolved IP. Workarounds • Upgrade to the patched version. • Enable authentication (`CRAWL4AI_API_TOKEN`). • Restrict the container's outbound network access (egress firewall / no metadata route). Credits Internal security audit (Crawl4AI maintainers).