AIKIDO-2026-317735
rmcp is vulnerable to Server-Side Request Forgery (SSRF)
74
High Risk
This Affects:
rmcpTL;DR
The rmcp OAuth client in crates/rmcp/src/transport/auth.rs accepts a server-controlled resource_metadata URL from the WWW-Authenticate header and fetches it without same-origin or private-network validation. An attacker-controlled or compromised MCP server can return a 401 response pointing the client at loopback, RFC 1918, link-local, or cloud metadata endpoints, causing an outbound request from the victim application's network context. This allows server-side request forgery against internal services and cloud metadata endpoints. The fix enforces same-origin resource metadata URLs and blocks loopback, private, link-local, and known cloud metadata hosts.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application uses the rmcp OAuth client to connect to MCP servers.
Background info
rmcp is vulnerable to Server-Side Request Forgery (SSRF) in versions 0.8.2 - 1.8.0.
How to fix this
Upgrade the rmcp library to the patch version.
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