CVE-2026-42271
Impact
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.
Patches
Fixed in 1.83.7. Both test endpoints now require the PROXY_ADMIN role, bringing them into line with the save endpoint.
Workarounds
If upgrading is not immediately possible, developers should block POST /mcp-rest/test/connection and POST /mcp-rest/test/tools/list at their reverse proxy or API gateway.
Package Versions Affected
Automatically patch vulnerabilities without upgrading
CVSS Version
Related Resources
References
https://github.com/BerriAI/litellm/security/advisories/GHSA-v4p8-mg3p-g94g, https://github.com/BerriAI/litellm, https://github.com/BerriAI/litellm/releases/tag/v1.83.7-stable
Basic Information
