DeepSeek Harness prior to 0.1.2-alpha.2, and specifically commit 3e24087, contains a missing authentication vulnerability in its web profile HTTP and WebSocket RPC control plane, allowing any local process, including those running as a different OS user, to reach unauthenticated session methods such as session.create and session.prompt. Attackers can invoke session.prompt to trigger the agent's bash and filesystem tools, achieve arbitrary command execution as the victim user using their configured model credentials, intercept live session traffic and logs over the event mux stream, and bypass human tool-approval checks via POST /api/respond by matching only rpcId, approvalId, and sessionId values broadcast over the ungated stream.