{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-64684","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","state":"PUBLISHED","assignerShortName":"GitHub_M","dateReserved":"2026-07-20T17:12:12.892Z","datePublished":"2026-09-16T21:18:48.886Z","dateUpdated":"2026-09-19T01:56:51.763Z"},"containers":{"cna":{"title":"RMCP: Custom HTTP headers leak to cross-origin redirect targets","problemTypes":[{"descriptions":[{"cweId":"CWE-200","lang":"en","description":"CWE-200: Exposure of Sensitive Information to an Unauthorized Actor","type":"CWE"}]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":6.8,"baseSeverity":"MEDIUM","confidentialityImpact":"HIGH","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"CHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N","version":"3.1"}}],"references":[{"name":"https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc","tags":["x_refsource_CONFIRM"],"url":"https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc"},{"name":"https://github.com/modelcontextprotocol/rust-sdk/pull/936","tags":["x_refsource_MISC"],"url":"https://github.com/modelcontextprotocol/rust-sdk/pull/936"},{"name":"https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b","tags":["x_refsource_MISC"],"url":"https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b"},{"name":"https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0","tags":["x_refsource_MISC"],"url":"https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0"}],"affected":[{"vendor":"modelcontextprotocol","product":"rust-sdk","versions":[{"version":"< 2.1.0","status":"affected"}]}],"providerMetadata":{"orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M","dateUpdated":"2026-09-16T21:18:48.886Z"},"descriptions":[{"lang":"en","value":"RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.1.0, the rmcp crate's StreamableHttpClientTransport in crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs builds its default_http_client with reqwest's automatic redirect policy and applies caller-supplied values from StreamableHttpClientTransportConfig.custom_headers without marking them as sensitive. When a malicious or compromised MCP endpoint returns a cross-origin 307 or 308 redirect, reqwest follows the redirect and apply_custom_headers causes custom API keys or authentication tokens to be replayed to the new origin, where an attacker can capture and reuse them. The separate auth_header path is not affected because it uses the standard Authorization header, which reqwest strips on cross-origin redirects. This issue is fixed in version 2.1.0."}],"source":{"advisory":"GHSA-9g45-5xwm-f3wc","discovery":"UNKNOWN"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-19T01:56:38.766580Z","id":"CVE-2026-64684","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-09-19T01:56:51.763Z"}}]}}