debugmcp mcp-debugger server.ts handleGetSourceContext path traversal

Vulnerability

A path traversal vulnerability exists in debugmcp/mcp-debugger through version 0.20.0. The handleGetSourceContext function in src/server.ts accepts a user-controlled file argument. In host mode, resolvePathForRuntime returns the input path unchanged, and no workspace-boundary enforcement is applied before file operations [1]. This allows an attacker to read arbitrary files on the filesystem.

Exploitation

An attacker can send a crafted source-context request to the MCP tool endpoint, supplying an arbitrary file path (e.g., /etc/passwd) as the file parameter. The server validates the session (if any) but then proceeds to check the file existence and read its contents, effectively leaking the file's data to the attacker [1]. No special privileges are required beyond network access to the service.

Impact

Successful exploitation allows an attacker to read arbitrary files from the server filesystem, leading to information disclosure. This can expose sensitive configuration, source code, credentials, or other confidential data.

Mitigation

As of the latest information, the vendor has not responded to disclosure and no patch is available [1]. Users should monitor the repository for updates. Until a fix is released, mitigate by restricting network access to the affected service or implementing input validation to prevent path traversal (e.g., block absolute paths and ../ sequences).