CVE-2026-59822

BerriAI LiteLLM, a widely used self-hosted AI gateway and proxy server for calling LLM APIs, fails to properly authenticate requests to its MCP Streamable HTTP endpoint in versions prior to 1.84.0. An unauthenticated attacker can send a fabricated Authorization header that triggers an OAuth2 passthrough fallback, which replaces failed LiteLLM key validation with an empty UserAPIKeyAuth() object and lets the request reach MCP tooling without any valid LiteLLM key. Successful exploitation grants unauthenticated access to the gateway's MCP tooling with high confidentiality impact per the CVSS 4.0 score of 8.8, and public reporting describes attackers chaining LiteLLM weaknesses from authentication bypass to root code execution and cloud credential theft. Any organization running LiteLLM before 1.84.0 is affected, particularly gateways exposed to the internet. The flaw is confirmed exploited in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2026-09-02, while EPSS currently estimates a 0.9% probability of exploitation in the next 30 days.

What to do: Upgrade LiteLLM to version 1.84.0 or later immediately, in line with the CISA KEV required action and BOD 26-04 guidance for internet-exposed assets. Audit whether the MCP endpoint is reachable from the internet and check for signs of exploitation, including unexpected MCP tool calls, use of fabricated Authorization headers, and use of default or example admin keys such as 'sk-1234'. Until patched, restrict access to the MCP endpoint and review cloud credentials accessible from the gateway host for signs of theft or root-level activity.