{"id":"CVE-2026-63118","state":"PUBLISHED","title":"MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection","description":"MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.","publishedAt":"2026-07-29T19:07:33.452Z","updatedAt":"2026-07-29T19:35:10.375Z","severity":{"score":6.9,"label":"Medium","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["modelcontextprotocol ruby-sdk"],"affected":[{"vendor":"modelcontextprotocol","product":"ruby-sdk","versions":[{"version":"< 0.23.0","status":"affected"}]}],"references":["https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m","https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a","https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0"],"weaknesses":["CWE-346","CWE-350"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63118.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63118","state":"PUBLISHED","datePublished":"2026-07-29T19:07:33.452Z","dateUpdated":"2026-07-29T19:35:10.375Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-07-15T16:54:55.816Z"},"containers":{"cna":{"title":"MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection","descriptions":[{"lang":"en","value":"MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0."}],"affected":[{"vendor":"modelcontextprotocol","product":"ruby-sdk","versions":[{"version":"< 0.23.0","status":"affected"}]}],"references":[{"url":"https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m","name":"https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a","name":"https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a","tags":["x_refsource_MISC"]},{"url":"https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0","name":"https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"ACTIVE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"HIGH","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":6.9,"baseSeverity":"MEDIUM","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N","version":"4.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-346","lang":"en","description":"CWE-346: Origin Validation Error","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-350","lang":"en","description":"CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-07-29T19:07:33.452Z"},"source":{"advisory":"GHSA-rjr6-rcgv-9m7m","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-07-29T19:34:40.295615Z","id":"CVE-2026-63118","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-07-29T19:35:10.375Z"}}]}}}