CVE-2026-59822: BerriAI LiteLLM Improper Authentication Vulnerability

High severity, CVSS 8.2. Actively exploited: in CISA KEV since 2026-09-02. EPSS: 0.8% chance of exploitation in the next 30 days.

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Affected products

• LiteLLM LiteLLM: before 1.84.0 (fixed in 1.84.0)

Published 2026-07-08. Last modified 2026-09-03.