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CVE-2026-59822

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

CVSS 4.0 High 8.8Known exploited (CISA KEV)

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

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.

Official description from the CVE record, published by GitHub_M. Copyright © 1999-2026 The MITRE Corporation. See /security/cve/legal for the CVE license. View the record on cve.org

Key data

CVSS 4.0 High 8.8
Score published by GitHub_M in the CVE record.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

  • Attack vector: Network

    The vulnerable component can be reached over a network, possibly from the Internet.

  • Attack complexity: Low

    No measurable action is needed to get around the system's built-in security controls. The attack is repeatable.

  • Attack requirements: None

    The attack works without any special deployment or execution conditions.

  • Privileges required: None

    No account or privileges are needed.

  • User interaction: None

    No action from any user is needed.

  • Vulnerable system: confidentiality: High

    Serious or total effect on the secrecy of data.

  • Vulnerable system: integrity: Low

    Limited effect on the trustworthiness of data.

  • Vulnerable system: availability: None

    No effect on availability.

  • Subsequent systems: confidentiality: None

    No effect on other systems' data secrecy.

  • Subsequent systems: integrity: None

    No effect on other systems' data trustworthiness.

  • Subsequent systems: availability: None

    No effect on other systems' availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS
Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.
Score
0.00836 (0.8% probability)
Percentile
58.0%
Scores of
Nov 10, 2026
Model
v2026.06.15
CISA Known Exploited Vulnerabilities
This CVE is listed in the CISA KEV catalog.
Name in the catalog
BerriAI LiteLLM Improper Authentication Vulnerability
Added to the catalog
Sep 2, 2026
Federal due date
Sep 16, 2026
CISA assessment as of Sep 2, 2026
Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.
Exploitation
Recorded by CISA as active
Automatable
yes
Technical impact
partial
Weakness (CWE)
CWE catalog version 5.0.
CWE names: Copyright © 2006-2026, The MITRE Corporation. See /security/cve/legal for the CWE license.
  • CWE-287Improper Authentication
  • CWE-306Missing Authentication for Critical Functionality
Affected products
Products listed in the CVE record, as the CNA published them.

  • BerriAI litellm

    • affected: < 1.84.0
References
Links listed in the CVE record. They lead to other sites, which CubePath does not control.
Timeline
  1. ID reserved
  2. Record published
  3. Added to CISA KEV
  4. Record last updated

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:07 UTC. Sources and licenses