Vulnerability Description
RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c
- https://github.com/modelcontextprotocol/rust-sdk/issues/815
- https://github.com/modelcontextprotocol/rust-sdk/issues/822
- https://github.com/modelcontextprotocol/rust-sdk/pull/764
- https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x
FAQ
What is CVE-2026-42559?
CVE-2026-42559 is a vulnerability with a CVSS score of 8.8 (HIGH). RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not valid...
How severe is CVE-2026-42559?
CVE-2026-42559 has been rated HIGH with a CVSS base score of 8.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-42559?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.