Vulnerability Analysis
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
Exploitability:-
Impact Score:-
Temporal Score:-
EPSS:0.52%
Threat Intelligence Signals
CISA KEV
YES
KEV Date Added
2026-09-02
Ransomware Use
Unknown
KEV Due Date
2026-09-16
VulnCheck In-the-Wild
No
Nuclei Template
No
EPSS Score
0.516%
EPSS Percentile
41.9th pct
GHSA ID
GitHub Severity
HIGH
SSVC Exploitation
Active
SSVC Automatable
Yes
Vulnerability Class
Authentication Bypass
Identity & Timeline
| Status | - |
| Assigning Authority | - |
| Discovered Via | - |
| Record Completeness | - |
| CVSS Version / Source | - |
| Reserved | - |
| Published | - |
| Patch Date (date_public) | - |
| Exploit DB Date | - |
| First GitHub PoC Date | - |
| Last Updated | - |
| Time to Patch (Days to fix) | - |
| Exploit Release Gap | - |
| PoC Release Gap | - |
| Exploit DB References | None identified |
Affected Products & Versions
| Vendor | Product | Affected Versions |
|---|---|---|
| No affected products specified. | ||
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