PYSEC-2026-3479

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

Description

### Impact LiteLLM's MCP Streamable HTTP endpoint could allow an unauthenticated attacker to establish an authenticated MCP session using an arbitrary Bearer token. The MCP auth handler supported OAuth2 passthrough for upstream MCP servers, but the fallback path could replace failed LiteLLM key validation with an empty `UserAPIKeyAuth()` object. This allowed requests with a fabricated `Authorization` header to reach MCP tooling without a valid LiteLLM key. An attacker could use this to list and call configured MCP tools and access connected services exposed through MCP. ### Patches The issue is fixed in `1.84.0`. We recommend upgrading to `1.84.0` or later. ### Workarounds If upgrading is not immediately possible, disable MCP routes or block access to `/mcp/` and related MCP endpoints at your reverse proxy or API gateway. ### References * [v1.84.0](https://github.com/BerriAI/litellm/releases/tag/v1.84.0)

Affected packages

References

• https://github.com/BerriAI/litellm/security/advisories/GHSA-7488-6r32-c95q WEB
• https://nvd.nist.gov/vuln/detail/CVE-2026-59822 ADVISORY
• https://github.com/BerriAI/litellm/pull/26463 WEB
• https://github.com/BerriAI/litellm/commit/73869f0faf7d11ee21adcb5f91b8c33a340b6c2c WEB
• https://github.com/BerriAI/litellm PACKAGE
• https://github.com/BerriAI/litellm/releases/tag/v1.84.0 WEB
• https://pypi.org/project/litellm PACKAGE
• https://github.com/advisories/GHSA-7488-6r32-c95q ADVISORY

Sources