Summary
LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback
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
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.
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The issue is fixed in 1.84.0.
We recommend upgrading to 1.84.0 or later.
Frequently Asked Questions
- What is CVE-2026-59822? CVE-2026-59822 is a high-severity improper authentication vulnerability in litellm (pip), affecting versions < 1.84.0. It is fixed in 1.84.0. The application does not adequately verify the identity of a user, device, or process before granting access.
- Which versions of litellm are affected by CVE-2026-59822? litellm (pip) versions < 1.84.0 is affected.
- Is there a fix for CVE-2026-59822? Yes. CVE-2026-59822 is fixed in 1.84.0. Upgrade to this version or later.
- Is CVE-2026-59822 exploitable, and should I be worried? Whether CVE-2026-59822 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59822 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59822? Upgrade
litellmto 1.84.0 or later.