CVE-2026-64684 with a CVSS score of 6.8 is a vulnerability in the rmcp crate where the StreamableHttpClientTransport forwards custom HTTP headers to cross-origin redirect targets because automatic redirect handling does not remove headers configured through custom_headers. An attacker who controls or compromises the original MCP server can issue a 307 or 308 redirect to an attacker-controlled server and capture sensitive headers such as X-API-Key or X-Auth-Token potentially enabling unauthorized access to the MCP server. The vulnerability is addressed by disabling automatic redirect following so redirects can be handled with appropriate header protection.
The following reports contain further technical details:[/subscribe_to_unlock_form]
CVE-2026-64684 with a CVSS score of 6.8 is a vulnerability in the rmcp crate where the StreamableHttpClientTransport forwards custom HTTP headers to cross-origin redirect targets because automatic redirect handling does not remove headers configured through custom_headers. An attacker who controls or compromises the original MCP server can issue a 307 or 308 redirect to an attacker-controlled server and capture sensitive headers such as X-API-Key or X-Auth-Token potentially enabling unauthorized access to the MCP server. The vulnerability is addressed by disabling automatic redirect following so redirects can be handled with appropriate header protection.
The following reports contain further technical details:[emaillocker id="1283"]
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