CVE-2026-35030: berriai litellm Improper Authentication

Vulnerability summary

CVE-2026-35030 is a critical (CVSS 9.4) Improper Authentication vulnerability in berriai litellm. EPSS estimates a 0.88% chance of exploitation in the next 30 days, higher than 58.4% of scored vulnerabilities.

Timeline

1. 06-04-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

Description

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.83.0, when JWT authentication is enabled (enable_jwt_auth: true), the OIDC userinfo cache uses token[:20] as the cache key. JWT headers produced by the same signing algorithm generate identical first 20 characters. This configuration option is not enabled by default. Most instances are not affected. An unauthenticated attacker can craft a token whose first 20 characters match a legitimate user's cached token. On cache hit, the attacker inherits the legitimate user's identity and permissions. This affects deployments with JWT/OIDC authentication enabled. Fixed in v1.83.0.

• CWE-287Improper AuthenticationWhen an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
• CWE-222Truncation of Security-relevant InformationThe product truncates the display, recording, or processing of security-relevant information in a way that can obscure the source or nature of an attack.