Authentication Bypass Using an Alternate Path or Channel Affecting litellm package, versions [,1.81.16)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-LITELLM-17391912
- published21 Jun 2026
- disclosed21 Jun 2026
- creditEdward-x
Introduced: 21 Jun 2026
NewCVE-2026-12773 (opens in a new tab)How to fix?
Upgrade litellm to version 1.81.16 or higher.
Overview
litellm is a Library to easily interface with LLM API providers
Affected versions of this package are vulnerable to Authentication Bypass Using an Alternate Path or Channel via exception handling in the MCP proxy authentication flow. An attacker can bypass authentication by supplying an arbitrary invalid token in the Authorization header. When API key validation raises a 401 or 403 exception, the exception is incorrectly swallowed and a default UserAPIKeyAuth object is created, allowing unauthenticated access to backend MCP servers configured with allow_all_keys: true. This may enable unauthorized access to data, execution of sensitive tools, or remote code execution depending on the capabilities exposed by the backend MCP servers.
Note: Exploitation requires at least one backend MCP server to be configured with allow_all_keys: true.