CVE-2026-35030: LiteLLM has an authentication bypass via OIDC userinfo cache key collision

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-06 · updated 2026-10-24
Weakness: CWE-287

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.

Affected products

BerriAI litellm: before 1.83.0 — fixed in 1.83.0

How to fix

Upgrade to a fixed version: BerriAI litellm 1.83.0. Check the vendor advisory for mitigations.

References

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