CVE-2026-111769: MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
In affected versions, the SDK’s HTTP client transports and OAuth requests followed redirects to any origin.
If an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an X-API-Key set in requestInit.headers) and the mcp-session-id header. On a 307 or 308 it also received the request body, including OAuth token requests with their refresh_token and client_secret.
On current runtimes fetch already drops the Authorization header across origins.
References
- github.com/advisories/GHSA-6prh-2h8m-c8cw
- github.com/modelcontextprotocol/typescript-sdk/commit/30bfe5139f4b0825c90cd725f9a7e3f9af5e120d
- github.com/modelcontextprotocol/typescript-sdk/commit/433eb413dc305ebeb93b8ebcde0095a8fc0d5fa0
- github.com/modelcontextprotocol/typescript-sdk/pull/2901
- github.com/modelcontextprotocol/typescript-sdk/pull/2902
- github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-6prh-2h8m-c8cw
- nvd.nist.gov/vuln/detail/CVE-2026-111769
Code Behaviors & Features
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