Vulnerability in modelcontextprotocol rust-sdk

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's OAuth implementation in crates/rmcp/src/transport/auth.rs omits the RFC 9728 resource field from ResourceServerMetadata and allows discover_oauth_server_via_resource_metadata to use protected-resource metadata without confirming that the returned resource identifier exactly matches the configured MCP server. A malicious MCP server can publish metadata for a different legitimate MCP resource and its authorization server, causing a victim who connects and completes the authorization flow to obtain a legitimate access token that the client subsequently sends to the malicious server. The attacker can capture the token and impersonate the victim against the legitimate MCP resource within the token's granted scopes. This issue is fixed in version 2.0.0.

[ Fixes ]Fixes and patches

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ Advisories ]Government CERT advisories

• BSI CERT-Bund12 Oct 2026WID-SEC-2026-3883

  Red Hat Enterprise Linux (goose, environment-modules, tornado): Multiple vulnerabilities Translated from German

  Risk highCVE-2026-93599CVE-2026-63128CVE-2026-103262+3 more CVEs

[ References ]References

• github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwjx_refsource_CONFIRM
• github.com/modelcontextprotocol/rust-sdk/pull/937x_refsource_MISC
• github.com/modelcontextprotocol/rust-sdk/commit/c1a8b29ff2cc45e7820b900dae42cbb4958089ecx_refsource_MISC
• github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0x_refsource_MISC