2026-04-15 · 2026-Q2
LiteLLM OIDC Userinfo Cache Authentication Bypass
PrimaryL6Identity / RunSecondaryL1Credential
- Fixable:
- Yes, vendor patch
- Vendor response:
- Unknown
- In the wild:
- No
- Actor:
- Attacker
Target
LiteLLM (BerriAI LLM gateway) deployments with JWT auth enabled
Impact
Unauthenticated attacker can craft a token whose first 20 characters collide with a cached legitimate token, inheriting that user's identity and permissions across the gateway
Root Cause
OIDC userinfo cache keyed on token[:20] instead of the full token or a secure hash; JWTs produced by the same signing algorithm share the same header prefix