Описание
9router: Unauthenticated LLM proxy access via /codex rewrite authorization bypass
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:
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:
The rewrite configuration then maps the allowed request to the protected backend route:
The backend route reaches the same handler used by the canonical LLM endpoint:
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
Observed result:
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
Observed result:
The request reaches the LLM backend without an API key.
A controlled upstream provider endpoint recorded the outbound request from 9router:
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
Observed result:
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
Observed result:
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
- A remote attacker identifies a publicly reachable 9router instance.
- The attacker sends LLM proxy requests to
/codex/*instead of/api/v1/responses. - The middleware evaluates the original
/codex/*path and does not apply the LLM API-key gate. - The rewrite maps the request to
/api/v1/responses. - The backend processes the request and performs an upstream provider call.
- 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.
Пакеты
9router
< 0.5.2
0.5.2
Связанные уязвимости
9Router is an AI router & token saver. Prior to 0.5.2, 9router protects /v1, /v1beta, /api/v1, and /api/v1beta in src/dashboardGuard.js but omits /codex before next.config.mjs rewrites /codex/* to /api/v1/responses. A remote unauthenticated attacker can send requests to /codex/* to bypass the API-key gate and cause the server to make upstream provider calls using operator-stored LLM provider credentials. This issue is fixed in version 0.5.2.