{"cve":"CVE-2026-64684","nvd":{"published":"2026-09-16T22:17:04.577","modified":"2026-09-23T18:12:04.247","status":"Awaiting Analysis","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N","score":6.8},"cwes":["CWE-200"],"references":["https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b","https://github.com/modelcontextprotocol/rust-sdk/pull/936","https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0","https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:54:41.405518556+00:00"},"epss":{"cve":"CVE-2026-64684","score":0.005,"percentile":0.42848,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-9g45-5xwm-f3wc","url":"https://osv.dev/vulnerability/GHSA-9g45-5xwm-f3wc","summary":"RMCP: Custom HTTP headers leak to cross-origin redirect targets","modified":"2026-09-17T16:45:06.215938994Z","packages":[{"ecosystem":"crates.io","name":"rmcp","purl":"pkg:cargo/rmcp","ranges":["<2.1.0"],"fixed":["2.1.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}