Answer in brief
CVE-2026-111769 records a Medium severity (CVSS 6.5) vulnerability in MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies. The current sources do not mark it as known exploited. The current feed maps @modelcontextprotocol/client (npm), @modelcontextprotocol/sdk (npm). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps @modelcontextprotocol/client (npm), @modelcontextprotocol/sdk (npm). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| @modelcontextprotocol/clientnpm | >=2.0.0,<2.3.0 | 2.3.0 |
| @modelcontextprotocol/sdknpm | <1.32.0 | 1.32.0 |
Published upstream
Oct 20, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Oct 20, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Oct 20, 2026
### Summary 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. ### Am I affected? Yes, if your application uses `StreamableHTTPClientTransport`, `SSEClientTransport`, or the SDK's OAuth client functions such as `auth()`. stdio clients are not affected. Affected versions: - `@modelcontextprotocol/sdk` all versions through 1.31.0 - `@modelcontextprotocol/client` 2.0.0 through 2.2.0 ### Fix Upgrade to: - 1.x: `@modelcontextprotocol/sdk` 1.32.0 or later - 2.x: `@modelcontextprotocol/client` 2.3.0 or later Redirects are now followed only within the same origin, and not at all in browsers. If your MCP server or authorization server redirects to another origin on purpose, configure the final URL instead. Setting `redirectPolicy: 'follow'` on a transport restores the old behaviour and the exposure. If a redirect may have reached a host you do not control, rotate the API keys and `client_secret` your application held and revoke its tokens. If you cannot upgrade yet, pass a `fetch` that refuses redirects, for example `(url, init) => fetch(url, { ...init, redirect: 'error' })`.
Quoted source text, attributed separately from HOL analysis.