CVE-2026-85709

The LightRAG API server passes raw Python exception messages directly into HTTP
error responses across 30+ error handlers in every router. When combined with
the default unauthenticated configuration (see companion report on CWE-306), any
network-reachable client can trigger exceptions whose raw text discloses
internal infrastructure, server filesystem paths, database host/port/user, LLM
provider error details, and Python library internals. No global exception
handler sanitizes error messages before they reach the client.

Details

Throughout the API route handlers, exceptions are caught and their string
representation is returned verbatim via detail=str(e) / detail=str(exc)
(and f-string variants such as detail=f"...: {str(e)}"). This occurs in every
router file. Location breakdown on the current main branch:

HTTP 500, raw exception passthrough (except Exception as e):

• document_routes.py, 13
• graph_routes.py, 12 (mix of detail=f"...{str(e)}" and detail=error_msg)
• query_routes.py, 3
• ollama_api.py, 2
• lightrag_server.py, 1 (health endpoint)

HTTP 422, raw exception passthrough (except ValueError as exc):

• document_routes.py, 2 (chunking-config validation)

Total: ~33 raw-exception-to-HTTP-response locations. The only pre-existing
custom exception handler in lightrag_server.py is specific to
RequestValidationError for /query/data; it does not cover the generic
Exception handlers in route code.

Example pattern (document_routes.py, upload handler):

except Exception as e:
    logger.error(f"Error /documents/upload: {file.filename}: {str(e)}")
    raise HTTPException(status_code=500, detail=str(e))

Categories of sensitive information that can leak through these responses:

1. Server filesystem paths. File-I/O errors from the default JSON storage
   backend expose the server's directory layout
   (e.g. [Errno 13] Permission denied: '/app/data/rag_storage/default/kv_store_full_docs.json'),
   aiding path-traversal or targeted attacks. (Verified, see PoC Step 1.)

2. Database host / port / user / database name. Connection errors from the
   PostgreSQL, MongoDB, Redis, or Neo4j backends surface the target the driver
   was trying to reach, e.g. asyncpg raises
   password authentication failed for user "lightrag" (username) or a socket
   error naming the unreachable host and port.
   Note on credentials: the PostgreSQL backend uses asyncpg, which is
   built from keyword parameters and does not echo the password in its
   exception strings, so a raw asyncpg error leaks host/port/user/db, not the
   password. URI-configured backends behave differently: the MongoDB backend is
   built with AsyncMongoClient(MONGO_URI, ...), and a malformed-URI /
   configuration error from pymongo can surface the connection string itself,
   which may embed credentials (mongodb://user:password@host:port/). The leak
   surface is therefore backend- and error-type-dependent.

3. LLM provider error details. Errors from OpenAI / Gemini / Bedrock and
   other providers may include model names, organization ids, or partial API
   error context that reveal the deployment.

4. Python library internals. Unexpected exceptions expose class names,
   library-internal messages, and stack fragments that fingerprint the server
   stack and version.

5. Configuration details. Errors during configuration/parsing may reveal
   storage backend types and other configuration values.

The risk is amplified by the default unauthenticated configuration (CWE-306,
companion report), which lets any network client trigger and read these errors
without credentials.

PoC

Tested on a clean checkout with the [api] extras installed and the server run
via lightrag-server.

Step 1, Filesystem path disclosure (default JSON storage)

With the default storage backend, a file-permission error is returned verbatim:

# Make a storage file unreadable to force an I/O error.
chmod 000 ./rag_storage/default/kv_store_full_docs.json
curl -s http://localhost:9621/documents | python3 -m json.tool

Vulnerable response, the full server-side path is disclosed:

{
    "detail": "[Errno 13] Permission denied: '/app/data/rag_storage/default/kv_store_full_docs.json'"
}

Step 2, Database infrastructure disclosure (PostgreSQL backend)

Configure a PostgreSQL KV backend pointed at an unreachable / misconfigured host:

LIGHTRAG_KV_STORAGE=PGKVStorage
POSTGRES_HOST=nonexistent-host-12345.example.com
POSTGRES_PORT=5432
POSTGRES_USER=lightrag
POSTGRES_DATABASE=lightrag

A request that touches storage returns the raw connection error, disclosing the
host / port / user the server is configured to reach (the asyncpg password is
not echoed, see the credentials note above):

{
    "detail": "[Errno -2] Name or service not known"
}

For a URI-configured backend such as MongoDB (MONGO_URI=mongodb://user:pass@host:port/db),
a malformed-URI / configuration error can instead surface the connection string
itself, including any embedded credentials.

Suggested remediation

1. Replace every detail=str(e) / detail=str(exc) pattern with a generic
   client message. Log the full exception server-side (message + traceback) and
   return only a generic message plus a correlation id:

   except Exception as e:
       logger.error(f"Error /documents/upload: {file.filename}: {e!r}")
       raise HTTPException(status_code=500, detail="Internal server error")
   

2. Register a last-resort global handler as defense-in-depth so any
   exception that escapes a route is sanitized identically:

   @app.exception_handler(Exception)
   async def unhandled_exception_handler(request, exc):
       logger.error(f"Unhandled exception: {exc!r}", exc_info=True)
       return JSONResponse(status_code=500, content={"detail": "Internal server error"})
   

3. Preserve genuine client-input validation feedback. The two HTTP 422
   chunking-config validators emit controlled, non-sensitive messages; keep them
   as 422 feedback rather than genericizing to 500, but wrap the raw exception
   so it is never a bare passthrough.

Fix status: implemented in HKUDS/LightRAG#3422, a shared
internal_server_error() helper routes all 500 handlers through a generic body
carrying a correlation id (full detail logged server-side), a global
@app.exception_handler(Exception) is registered in create_app, and the two
422 validators are wrapped.

Credits

• Thai Son Dinh from VinSOC Labs (R&D)
• Nguyen Huy Vu Dung from VinSOC Labs (AppSec)