Open WebUI: Any authenticated user can reach internal services and cloud metadata via NAT64-encoded URLs

Summary

Open WebUI fetches user-supplied URLs on the server for RAG URL ingestion, URL-to-markdown conversion and web-search content retrieval, and decides whether a destination is allowed by asking whether its IP address is globally routable. That test operates on the literal IPv6 address and does not look at the IPv4 address embedded inside it. On a deployment whose network has a NAT64 gateway, any verified user can wrap an internal or cloud-metadata IPv4 address in the NAT64 well-known prefix, pass the filter, and receive the internal response body back through the API.

Preconditions

• Any verified (authenticated) user account. No admin role, no elevated permission.
• Default configuration: ENABLE_LOCAL_WEB_FETCH off, the default WEB_FETCH_FILTER_LIST metadata blocklist in place. Neither prevents this, because the blocklist matches hostname strings and the NAT64 literal is not one of them.
• The deployment's network must provide NAT64 translation for the well-known 64:ff9b::/96 prefix, which is the common default on IPv6-only and dual-stack cloud and Kubernetes networks.
• Deployments on IPv4-only networks, or on any network without a NAT64 gateway, are not affected: the address has nowhere to route.

Impact

On an affected network a low-privilege user can read GET responses from services the server can reach but the internet cannot: cloud instance metadata including IAM role credentials, loopback-bound admin surfaces, and internal APIs in the same VPC or cluster. The response body is returned to the caller, so this is full-read, not blind. Exploitation is not universal, it depends entirely on the deployment's network providing NAT64 translation, which is why the score carries high attack complexity. Deployments without NAT64 lose nothing here.

Fix

Fixed in v0.11.0 by commit 1717b493d. Address classification now unwraps the IPv4 embedded in IPv6 transition encodings before deciding whether a destination is global, and applies that at all three checkpoints. NAT64-wrapped public destinations continue to work. Upgrading to v0.11.0 fully resolves the issue with no configuration change.