CVE-2026-42271

CVE-2026-42271 is a high-severity vulnerability in Litellm with a CVSS 3.x base score of 8.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2026-06-08). The underlying weakness is classified as CWE-77.

Key facts

Description

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. From version 1.74.2 to before version 1.83.7, two endpoints used to preview an MCP server before saving it — POST /mcp-rest/test/connection and POST /mcp-rest/test/tools/list — accepted a full server configuration in the request body, including the command, args, and env fields used by the stdio transport. When called with a stdio configuration, the endpoints attempted to connect, which spawned the supplied command as a subprocess on the proxy host with the privileges of the proxy process. The endpoints were gated only by a valid proxy API key, with no role check. Any authenticated user — including holders of low-privilege internal-user keys — could therefore run arbitrary commands on the host. This issue has been patched in version 1.83.7.

Frequently asked questions

What is CVE-2026-42271?
LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. From version 1.74.2 to before version 1.83.7, two endpoints used to preview an MCP server before saving it — POST /mcp-rest/test/connection and POST /mcp-rest/test/tools/list — accepted a full server configuration in the request body, including the command, args, and env fields used by the stdio transport. When called with a stdio configuration, the endpoints attempted to connect, which spawned the supplied command as a subprocess on the proxy host with the privileges of the proxy process. The endpoints were gated only by a valid proxy API key, with no role check. Any authenticated user — including holders of low-privilege internal-user keys — could therefore run arbitrary commands on the host. This issue has been patched in version 1.83.7.
How severe is CVE-2026-42271?
CVE-2026-42271 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-42271 being actively exploited?
Yes. CVE-2026-42271 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-06-08, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2026-42271?
CVE-2026-42271 primarily affects Litellm. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-42271?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2026-42271 have an EU (EUVD) identifier?
Yes. CVE-2026-42271 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-28507. It is also flagged as exploited in the EUVD (since 2026-06-08).
When was CVE-2026-42271 published?
CVE-2026-42271 was published on 2026-05-08 and last updated on 2026-06-30.

References

Affected products (3)

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