{"id":"CVE-2026-64684","title":"RMCP is an official Rust SDK for the Model Context Protocol","summary":"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…","severity":"medium","cvss":6.8,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N","cwe":["CWE-200","CWE-212"],"vendor":"modelcontextprotocol","product":"rust-sdk","affected":["rust-sdk < 2.1.0"],"patched":["rmcp 2.1.0"],"published":"2026-09-16","updated":"2026-09-23","sourceUpdated":"2026-09-23T18:12:04.247","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-64684","references":[{"url":"https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b","label":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/pull/936","label":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0","label":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc","label":"security-advisories@github.com"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64684"},{"url":"https://github.com/modelcontextprotocol/rust-sdk"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64684.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-64684"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2535732"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-64684"},{"url":"https://github.com/advisories/GHSA-9g45-5xwm-f3wc"}],"tags":["nvd","cve.org","osv","rust","csaf","vex","red-hat","ghsa"],"epss":0.00395,"epssPercentile":0.33527,"aliases":["GHSA-9g45-5xwm-f3wc"],"ecosystem":"rust","ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-19T01:56:38.766580Z"},"ingestedAt":"2026-09-16T22:06:50.936Z","slug":"CVE-2026-64684","body":"## Overview\n\nRMCP 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-64684)\n\nAffected packages:\n\n- `rmcp < 2.1.0`\n\nPatched in:\n\n- `rmcp 2.1.0`\n\nSource: https://osv.dev/vulnerability/GHSA-9g45-5xwm-f3wc\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · updated 2026-09-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64684.json)","depth":"sunlit","depthScore":37,"depthScoreParts":{"impact":37.4,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}