SurrealDB: HTTP /rpc `sessions` method leaks attached session UUIDs, enabling full session hijack by anonymous callers

The HTTP /rpc sessions method returned every attached session UUID without authentication, and the /rpc handler accepted an arbitrary session field with no ownership check. An anonymous caller could enumerate UUIDs and impersonate any authenticated session.

"Attached" means sessions registered via {"method":"attach"} — the only writer to the HTTP session map. Ordinary stateless /rpc requests use ephemeral per-request sessions that are filtered from sessions() and destroyed at end-of-request, so they are not enumerable.

Exposure

• Exposed: clients that issue attach, notably the official Rust SDK's Http/Https engine (auto-attaches once per Surreal handle).
• Not exposed: REST endpoints (/sql, /key, /signin, /export, etc.); WebSocket /rpc (per-connection scope, attach refused); embedded / MCP usage; ad-hoc POST /rpc callers that never attach.

Impact

For each attached and authenticated session, an unauthenticated attacker can read, write, and delete any data the session can reach, dump metadata, invalidate sessions, and escalate to that session's privilege level (up to root). An attached session that has not yet authenticated is Level::No and confers no privilege.

Patches

1. HTTP sessions() now returns method_not_allowed. WebSocket retains per-connection enumeration.
2. The HTTP /rpc handler gates client-supplied session IDs against the caller's request-level auth principal (actor id + level); mismatches return session_not_found.
3. Attached HTTP sessions are capped via SURREAL_HTTP_MAX_ATTACHED_SESSIONS.

Versions 3.1.0 and later are not affected.

Workarounds

No configuration-level mitigation fully addresses this. For Users unable to upgrade:

• Avoid SDKs and client flows that call attach against HTTP /rpc (notably the Rust SDK's Http/Https engine). Prefer the WebSocket transport, or REST endpoints (/sql, /signin, /key, /export) which never populate the attached-session map.
• Restrict /rpc to trusted clients at the network layer.