{"id":"CVE-2026-42559","sourceIdentifier":"security-advisories@github.com","published":"2026-05-14T15:16:46.750","lastModified":"2026-06-17T10:48:02.220","vulnStatus":"Deferred","cveTags":[],"descriptions":[{"lang":"en","value":"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":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"modelcontextprotocol","product":"rust-sdk","versions":[{"version":"< 1.4.0","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","baseScore":8.8,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":2.8,"impactScore":5.9}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-14T16:00:22.834947Z","id":"CVE-2026-42559","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-346"},{"lang":"en","value":"CWE-350"}]}],"references":[{"url":"https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/issues/815","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/issues/822","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/pull/764","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx","source":"security-advisories@github.com"}]}