CVE-2026-116685

Name of the Vulnerable Software and Affected Versions Model Context Protocol Python SDK versions 1.8.0 through 1.29.1 Model Context Protocol Python SDK versions 2.0.0 through 2.1.1

Description Certain client paths in the SDK follow HTTP redirects to different origins, which can lead to the exposure of sensitive information. Specifically, when using streamable http client, streamablehttp client, sse client, ClientSessionGroup, OAuth, or the create mcp http client helper, the SDK forwards caller-supplied custom credential headers to the redirect destination. Additionally, for HTTP 307 or 308 responses, the request body is also forwarded. An attacker capable of influencing a trusted endpoint's redirect destination can capture these credentials and request bodies.

Recommendations Update Model Context Protocol Python SDK to version 1.30.0 or later for the 1.x branch. Update Model Context Protocol Python SDK to version 2.2.0 or later for the 2.x branch. As a temporary mitigation, provide a custom HTTP client with the follow redirects parameter set to False when using streamable http client (via http client) or sse client and streamablehttp client (via httpx client factory). Rotate any credentials that may have been exposed if the client previously followed a redirect to an untrusted host.