--- cve: "CVE-2026-64684" severity: "MEDIUM" cvss: 6.8 epss: "3.6%" vendor: "modelcontextprotocol" kev: false exploited: false published: "2026-09-16 22:17:04" tags: [cve, security, medium] source: tsecurity.de CVE-Dossier exported: "2026-09-18T08:39:40+02:00" --- # CVE-2026-64684 > 6.8 MEDIUM · 🧪 PoC ## Beschreibung 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-Vektor ``` CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N ``` | Metrik | Wert | Bewertung | |---|---|---| | AV Angriffsvektor | Netzwerk | bad | | AC Komplexität | Hoch | good | | PR Privilegien | Keine | bad | | UI Interaktion | Keine | bad | | S Scope | Verändert | bad | | C Vertraulichkeit | Hoch | bad | | I Integrität | Keine | good | | A Verfügbarkeit | Keine | good | ## Patch verfügbar (OSV) - 8e44af499bfa8d54f18fb475eb86a601a5a2e432 (Commit) ## Referenzen - - - - --- _Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-64684) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_