DeepSeek Harness before 0.1.2-alpha.1 contains an authentication bypass vulnerability that grants unauthenticated access to its local HTTP agent-control API by accepting a client-supplied loopback Host header in place of validating the actual TCP connection origin. On the default configuration, a confined tool-executed process can reach the loopback API without any port exposure and use it to escape its own OS sandbox, escalate to unconfined execution, and disable the approval prompt. When the port is externally reachable via tunnel, SSH forward, or reverse proxy, a remote attacker can exploit the same flaw to create sessions, execute arbitrary commands, and exfiltrate stored conversation transcripts without credentials.

DeepSeek Harness before 0.1.2-alpha.1 contains an authentication bypass vulnerability in its local HTTP control-plane API that allows attackers to gain full agent control by supplying a spoofed Host header, as the server validates only the client-supplied Host header value rather than the actual TCP connection origin. Attackers can exploit this flaw to invoke privileged commands such as commands/execute with danger-full-access permissions, escalate session approval policies to unconfined execution, and retrieve all stored conversations without any credential or API key.