CVE-2026-59822
LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback
Summary
### 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
| Ecosystem | Package | Affected versions | Fixed versions |
|---|---|---|---|
| PyPI | litellm | — | 1.84.0 |
Remediation: Upgrade to 1.84.0 or later.
References
Includes data from the GitHub Advisory Database, licensed under CC-BY 4.0.
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EPSS scores provided by the FIRST.org Exploit Prediction Scoring System.