CVE-2026-111769

Name of the Vulnerable Software and Affected Versions @modelcontextprotocol/sdk versions prior to 1.32.0 @modelcontextprotocol/client versions 2.0.0 through 2.2.0

Description HTTP client transports and OAuth client requests follow redirects to different origins while retaining custom request headers and the mcp-session-id header. For HTTP 307 or 308 responses, request bodies are also retained. This behavior affects StreamableHTTPClientTransport, SSEClientTransport, and OAuth client functions such as auth(). A malicious or compromised MCP or authorization server could exploit this to receive sensitive information, including API keys, session identifiers, OAuth refresh tokens, or OAuth client secrets. This occurs when a request is redirected to another origin.

Recommendations Update @modelcontextprotocol/sdk to version 1.32.0 or later. Update @modelcontextprotocol/client to version 2.3.0 or later. As a temporary workaround, use a fetch implementation that refuses redirects by setting redirect: 'error'. Rotate API keys and client secret values and revoke tokens if redirects may have reached an untrusted host.