Critical LiteLLM Host Header Flaw Enables Authentication Bypass

A critical vulnerability in LiteLLM tracked as CVE-2026-49468 allows attackers to bypass authentication through Host header injection and reach protected management endpoints. The flaw affects LiteLLM versions earlier than 1.84.0 and stems from a mismatch in how the authentication layer evaluates routes versus how FastAPI ultimately dispatches them, creating a path for unauthenticated access under specific conditions. The issue is classified as CWE-290 and has been rated CVSS 9.5, with researchers describing it as network-exploitable with low attack complexity and no user interaction required.

The vulnerability was responsibly disclosed by Le The Thang of KCSC and Kim Ngoc Chung of One Mount Group, and LiteLLM maintainers have released a fix in version 1.84.0 with no configuration changes required. There is no confirmed evidence of active exploitation, and LiteLLM Cloud customers are reportedly not affected. Self-hosted deployments may also be shielded if upstream infrastructure such as Cloudflare, WAFs, reverse proxies with strict allowlists, or host-validating load balancers normalize or reject malformed Host headers before requests reach the application.