Unauthenticated MCP tool access via swallowed exceptions
Published Jun 21, 2026 · Updated Jun 21, 2026
Improper authentication in LiteLLM 1.59.0 through 1.59.8 allows remote attackers to access MCP tools with a forged API token. The MCP Proxy process_mcp_request method catches 401 and 403 authentication exceptions, continues with a default UserAPIKeyAuth object, and routes the request. Exploitation requires a reachable MCP endpoint backed by a server configured with allow_all_keys; resulting access is limited by the tools exposed through that backend.
Summary
What happened
Improper authentication in LiteLLM 1.59.0 through 1.59.8 allows remote attackers to access MCP tools with a forged API token. The MCP Proxy process_mcp_request method catches 401 and 403 authentication exceptions, continues with a default UserAPIKeyAuth object, and routes the request. Exploitation requires a reachable MCP endpoint backed by a server configured with allow_all_keys; resulting access is limited by the tools exposed through that backend.
The record
- CVE
- CVE-2026-12773
- Published
- Jun 21, 2026
- Updated
- Jun 21, 2026
- Vendor
- Berri AI
- Product
- LiteLLM
- Classifications
- CWE-287, CWE-303, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 21, 2026CVE publishedPublication date reported by the CVE source.
- Jun 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.59.0
- Affected versionversion=1.59.1
- Affected versionversion=1.59.2
- Affected versionversion=1.59.3
- Affected versionversion=1.59.4
- Affected versionversion=1.59.5
- Affected versionversion=1.59.6
- Affected versionversion=1.59.7
- Affected versionversion=1.59.8
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- LiteLLM MCP authentication-bypass proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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