high8.8
CVE-2026-42559
rmcp Streamable HTTP server transport has a DNS rebinding vulnerability
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | rmcp | < 1.4.0 | 1.4.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-89vp-x53w-74fx
- https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx
- https://github.com/modelcontextprotocol/rust-sdk/issues/815
- https://github.com/modelcontextprotocol/rust-sdk/pull/764
- https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#security-warning
- https://nvd.nist.gov/vuln/detail/CVE-2026-42559
- https://github.com/modelcontextprotocol/rust-sdk/issues/822
- https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3
- https://github.com/nubo-db/dynoxide/security/advisories/GHSA-fvh2-gm75-j4j7
- https://rustsec.org/advisories/RUSTSEC-2026-0140.html