CVE-2026-59822

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

HIGH

8.2

CVSS Score

Published: July 8, 2026 at 07:32 PM UTC

Updated: October 25, 2026 at 05:10 PM UTC

2 products affected across 2 vendorsLiteLLMLiteLLM

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Severity

HIGH8.2

Exploitation

CISA KEV

Exploit prediction

EPSS 0.8%

SSVC

Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score0.8%

EPSS (Exploit Prediction Scoring System) estimates a 0.8% chance this CVE is exploited in the wild within the next 30 days — higher than 57% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

BerriAI LiteLLM contains an improper authentication vulnerability in the MCP Streamable HTTP endpoint that could allow an unauthenticated attacker to establish an authenticated MCP session using an arbitrary Bearer token.

Required Action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Ransomware Use

Unknown

Added to KEV

Sep 2, 2026

Remediation Due

Sep 16, 2026

40 days overdue

Notes

https://github.com/BerriAI/litellm/security/advisories/GHSA-7488-6r32-c95q

BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk

Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk

https://nvd.nist.gov/vuln/detail/CVE-2026-59822

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.