{"id":"CVE-2026-42559","aliases":["GHSA-89vp-x53w-74fx","GHSA-fvh2-gm75-j4j7","RUSTSEC-2026-0140","RUSTSEC-2026-0189"],"url":"https://o3.security/vulnerability/CVE-2026-42559","summary":"RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport","details":"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.","published":"2026-05-14T14:24:56.090Z","modified":"2026-08-07T11:51:06.430221348Z","cvss":{"score":8.8,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"rmcp","fixedVersion":"1.4.0"}],"fix":{"url":"https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3","label":"modelcontextprotocol/rust-sdk@8e22aa2"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42559.json"},{"type":"ADVISORY","url":"https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42559"},{"type":"REPORT","url":"https://github.com/modelcontextprotocol/rust-sdk/issues/815"},{"type":"REPORT","url":"https://github.com/modelcontextprotocol/rust-sdk/issues/822"},{"type":"FIX","url":"https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3"},{"type":"FIX","url":"https://github.com/modelcontextprotocol/rust-sdk/pull/764"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:51:06.430221348Z"}}