CVE-2026-42559: rmcp Streamable HTTP server transport has a DNS rebinding vulnerability
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 — violating the MCP specification’s transport security guidance.
References
- github.com/advisories/GHSA-89vp-x53w-74fx
- github.com/modelcontextprotocol/rust-sdk
- github.com/modelcontextprotocol/rust-sdk/issues/815
- github.com/modelcontextprotocol/rust-sdk/pull/764
- github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx
- modelcontextprotocol.io/specification/2025-06-18/basic/transports
- nvd.nist.gov/vuln/detail/CVE-2026-42559
Code Behaviors & Features
Detect and mitigate CVE-2026-42559 with GitLab Dependency Scanning
Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Learn more about Dependency Scanning →