A remote code execution flaw exists in Code Runner MCP Server when started with the --transport http option, exposing the /mcp JSON‑RPC endpoint without authentication on port 3088. An unauthenticated attacker can call run‑code to pass arbitrary source code, which the server executes through child_process.exec() using the language interpreter. The result is full execution of attacker‑supplied code with the privileges of the user running the server, meeting the criteria for a high‑severity denial of remote or local access vulnerability.

The vulnerability targets Code Runner MCP Server in all versions that support the --transport http flag. The unprotected JSON‑RPC endpoint is accessible directly on TCP port 3088 when the server is run with this option, regardless of the operating system or deployment environment.

The CVSS score of 8.7 indicates a high risk to confidentiality, integrity, and availability. Although no EPSS value is provided, the lack of authentication combined with the ability to execute arbitrary code makes exploitation likely in a network where the service is exposed. The issue is not currently listed in CISA KEV, but its severity warrants immediate attention. An attacker can remotely invoke the vulnerable endpoint, supply any source code, and cause it to run with local privileges, potentially compromising the entire host.