CVE-2026-63127

Name of the Vulnerable Software and Affected Versions rmcp versions prior to 2.0.0

Description The OAuth implementation in the rmcp crate fails to validate the resource parameter in OAuth Protected Resource metadata as required by RFC 9728. Specifically, the ResourceServerMetadata struct omits the resource field, and the discover oauth server via resource metadata() function processes protected-resource metadata without verifying that the returned resource identifier matches the configured MCP server. This allows a malicious MCP server to spoof metadata for a legitimate MCP resource and its authorization server. If a user connects to the malicious server and completes the authorization flow, the client sends a legitimate access token to the attacker's server. The attacker can then capture this token to impersonate the victim on the legitimate MCP resource within the granted scopes.

Recommendations Update to version 2.0.0.