CVE-2026-42271 PoC — LiteLLM: Authenticated command execution via MCP stdio test endpoints

Source

https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-42271.yaml

Associated Vulnerability

Title:LiteLLM: Authenticated command execution via MCP stdio test endpoints (CVE-2026-42271)
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.

Description

A critical unauthenticated remote code execution vulnerability exists in LiteLLM due to improper input handling in the MCP stdio test endpoint. An attacker can send a specially crafted request to the `/mcp-rest/test/connection` endpoint with controlled parameters, resulting in arbitrary command execution on the server. When combined with an authentication bypass technique—such as the Starlette BadHost flaw (CVE-2026-48710)—an unauthenticated attacker can exploit the chain to execute commands as the server process. Exploitation allows an attacker to spawn processes with the privileges of the LiteLLM server, potentially leading to complete compromise of the host.

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