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High

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

  • Disclosed: 22.07.2026
  • Updated: 11.10.2026 15:17

CISA confirms exploitation of this vulnerability in real attacks. Prioritise checking whether your application is affected. CISA KEV · CC0 1.0

Impact

LiteLLM's MCP Streamable HTTP endpoint could allow an unauthenticated attacker to establish an authenticated MCP session using an arbitrary Bearer token.

The MCP auth handler supported OAuth2 passthrough for upstream MCP servers, but the fallback path could replace failed LiteLLM key validation with an empty UserAPIKeyAuth() object. This allowed requests with a fabricated Authorization header to reach MCP tooling without a valid LiteLLM key.

An attacker could use this to list and call configured MCP tools and access connected services exposed through MCP.

Patches

The issue is fixed in 1.84.0.

We recommend upgrading to 1.84.0 or later.

Workarounds

If upgrading is not immediately possible, disable MCP routes or block access to /mcp/ and related MCP endpoints at your reverse proxy or API gateway.

References

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) litellm < 1.84.0 1.84.0

References

CVSS score -
CVSS vector
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
Weakness (CWE)
CWE-287
Platform
Python (PyPI)
Package
litellm
Disclosed
22.07.2026
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-3479 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-7488-6r32-c95q - CC BY 4.0

Vulnerability history: litellm

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (42) in the archive
Total entries
42
First → latest
04.2024 09.2026
Without a fix
14
Exploited in attacks
3

Severity breakdown

  • Critical 7
  • High 17
  • Medium 8
  • Low 9
  • Unrated 1

Disclosures per year

Severity:
  1. LiteLLM vulnerable to server-side template injection in the /prompts/test endpoint
    Critical · 9.8 CVE-2026-37004 < 1.83.7 1.83.7
  2. LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback this entry
    High Exploited in attacks CVE-2026-59822 < 1.84.0 1.84.0
  3. LiteLLM: Authentication Bypass via Host Header Injection
    Critical · 9.8 CVE-2026-49468 < 1.84.0 1.84.0
  4. LiteLLM allows a user to modify their own user_role via the /user/update endpoint
    High · 8.8 CVE-2026-47102 < 1.83.10 1.83.10
  5. LiteLLM allows an authenticated internal_user to create API keys with access to routes that their role does not permit
    High · 8.8 CVE-2026-47101 < 1.83.14 1.83.14
  6. LiteLLM has a sandbox escape in custom-code guardrail
    High · 8.8 CVE-2026-40217 >= 1.81.8, < 1.83.10 1.83.10
  7. LiteLLM: Authenticated command execution via MCP stdio test endpoints
    High · 8.8 Exploited in attacks CVE-2026-42271 >= 1.74.2, < 1.83.7 1.83.7
  8. LiteLLM has SQL Injection in Proxy API key verification
    Critical · 9.8 Exploited in attacks CVE-2026-42208 >= 1.81.16, < 1.83.7 1.83.7
  9. LiteLLM: Server-Side Template Injection in /prompts/test endpoint
    High CVE-2026-42203 >= 1.80.5, < 1.83.7 1.83.7
  10. LiteLLM: Password hash exposure and pass-the-hash authentication bypass
    High ghsa-69x8-hrgq-fjj8 < 1.83.0 1.83.0
  11. LiteLLM: Authentication bypass via OIDC userinfo cache key collision
    Critical CVE-2026-35030 < 1.83.0 1.83.0
  12. LiteLLM: Privilege escalation via unrestricted proxy configuration endpoint
    High CVE-2026-35029 < 1.83.0 1.83.0
  13. Two LiteLLM versions published containing credential harvesting malware
    Critical ghsa-5mg7-485q-xm76 >= 1.82.7, <= 1.82.8 no fix
  14. LiteLLM Has an Improper Authorization Vulnerability
    High · 8.1 CVE-2025-0628 < 1.61.15 1.61.15
  15. LiteLLM Has a Leakage of Langfuse API Keys
    High · 7.5 CVE-2025-0330 <= 1.52.1 no fix
  16. LiteLLM Reveals Portion of API Key via a Logging File
    High · 7.5 CVE-2024-9606 < 1.44.12 1.44.12
  17. LiteLLM Vulnerable to Denial of Service (DoS) via Crafted HTTP Request
    High · 7.5 CVE-2024-8984 < 1.56.2 1.56.2
  18. LiteLLM Vulnerable to Remote Code Execution (RCE)
    High · 8.8 CVE-2024-6825 >= 1.40.3.dev2, <= 1.40.12 no fix
  19. LiteLLM Vulnerable to Denial of Service (DoS)
    High · 7.5 CVE-2024-10188 < 1.53.1.dev1 1.53.1.dev1
  20. LiteLLM Server-Side Request Forgery (SSRF) vulnerability
    High · 7.5 CVE-2024-6587 < 1.44.8 1.44.8
  21. litellm vulnerable to remote code execution based on using eval unsafely
    Critical · 9.8 CVE-2024-5751 < 1.40.16 1.40.16
  22. Arbitrary file deletion in litellm
    High · 6.5 CVE-2024-4888 < 1.35.36 1.35.36
  23. litellm passes untrusted data to `eval` function without sanitization
    High · 7.2 CVE-2024-4264 <= 1.28.11 no fix
  24. LiteLLM has Server-Side Template Injection vulnerability in /completions endpoint
    Critical · 9.8 CVE-2024-2952 < 1.34.42 1.34.42

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