Vulnerability Intelligence Report
LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback
CVE-2026-59822
LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.
CISA KEV
SSVC: Active Exploitation
Automatable
Authentication Bypass
CVSS Base Score
8.8
HIGH
EPSS Probability:0.52%
Executive Threat Verdict
Evaluating...
Evaluating Threat Landscape...
Assessing known weaponization, exploitation telemetry, and federal advisories.
Attack Surface
—
Authentication
—
Weaponization
—
SSVC Action
—
Weaknesses (CWE)
Affected Products & Versions
| Vendor | Product | Affected Versions |
|---|---|---|
| BerriAI | litellm | < 1.84.0 (affected) |
References & Technical Advisories
No reference links found.
Threat Intelligence Signals
CISA KEV
ACTIVE IN CATALOG
EPSS Score
0.516%
GitHub Advisory
Vulnerability Class
Authentication Bypass
Identity & Timeline
| Status | PUBLISHED |
| Assigning Authority | GitHub, Inc. · Vendor · USA |
| Reserved | 2026-07-07T15:00:50 |
| Published | 2026-07-08T19:32:18 |
| Last Updated | 2026-09-03T03:56:05 |
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