appium-mcp-server versions through 0.1.61 contain a path traversal vulnerability in the write_file and write_files_batch tools. The server fails to validate or normalize file paths, allowing attackers to write files outside the intended PROJECT_ROOT directory. Attackers can exploit this by supplying absolute paths or relative paths containing parent directory segments (e.g., ../). This enables overwriting of arbitrary files with the privileges of the server user. Sensitive targets include shell profiles and configuration files located in the home directory. The vulnerability poses a significant risk as it can lead to privilege escalation or persistent backdoor installation. No authentication bypass is required beyond access to the MCP server tools.