CVE-2026-42559: rmcp Streamable HTTP server transport has a DNS rebinding vulnerability
(updated )
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/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3
- github.com/modelcontextprotocol/rust-sdk/issues/815
- github.com/modelcontextprotocol/rust-sdk/issues/822
- github.com/modelcontextprotocol/rust-sdk/pull/764
- github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx
- github.com/nubo-db/dynoxide/security/advisories/GHSA-fvh2-gm75-j4j7
- modelcontextprotocol.io/specification/2025-06-18/basic/transports
- nvd.nist.gov/vuln/detail/CVE-2026-42559
- rustsec.org/advisories/RUSTSEC-2026-0140.html
Code Behaviors & Features
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