MCPJam Inspector — a popular local-first development platform for building and testing MCP servers — contains a remote code execution vulnerability in versions 1.4.2 and earlier. A specially crafted HTTP request can trigger the unauthorized installation of an attacker-controlled MCP server on the target host.
By default, MCPJam Inspector binds to all network interfaces (0.0.0.0), not just localhost. Any attacker with network access to the host — including on a shared office or cloud development network — can send the malicious request without authentication.
Blast radius is high for developer environments: successful exploitation gives an attacker arbitrary code execution on the developer's machine, where MCP server source code, cloud credentials, API keys, and git history are typically present.
Immediate action: Upgrade to MCPJam Inspector v1.4.3. If you cannot upgrade, bind the inspector explicitly to 127.0.0.1 and ensure firewall rules block external access to its listening port.