LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback (CVE-2026-59822) | HOL Guard CVE

High · CVSS 8.8Known ExploitedCVE-2026-59822

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

Answer in brief

CVE-2026-59822 records a High severity (CVSS 8.8) vulnerability in LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback. The current sources mark it as known exploited. The current feed maps BerriAI/litellm (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 8, 2026Updated Sep 16, 2026Source checked Sep 21, 2026First seen by HOL Jul 8, 2026Material review Sep 16, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.8
Exploitation: Known exploited
Affected software: 2 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 8.8. Known-exploitation status makes exposure review time-sensitive. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps BerriAI/litellm (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:a:litellm:litellm::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
BerriAI/litellmgeneric	< 1.84.0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for BerriAI/litellm.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Jul 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 8, 2026
Added to CISA KEV
Sep 2, 2026
Evidence: source:kev:kev:kev:record

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.