CVE-2026-86121

Cua computer-server versions before 0.3.42 skip authentication entirely (CWE-306, missing authentication for a critical function) when the CONTAINER_NAME environment variable is unset, and the server binds to all network interfaces by default, yielding a critical 9.3 CVSS 4.0 score (network attack vector, no privileges or user interaction required). An unauthenticated attacker who can reach TCP port 8000 can invoke the run_command endpoint to execute arbitrary shell commands, read and write arbitrary files via the file-operation endpoints, and open interactive PTY shells, effectively giving full control of the host at the server's privilege level. Only deployments that run without CONTAINER_NAME set (for example bare-metal or ad hoc launches) are exposed this way, because containerized deployments that set the variable enforce authentication normally; affected operators are those running an affected version with port 8000 reachable from an untrusted network. There is no confirmed exploitation in the wild, no public proof-of-concept, the flaw is not in CISA's KEV, and EPSS estimates roughly a 0.6% probability of exploitation within 30 days.

What to do: Upgrade computer-server to 0.3.42 or later. As an interim mitigation, explicitly set the CONTAINER_NAME environment variable to restore authentication and restrict or firewall TCP port 8000, for example by binding the server to localhost. Audit any exposed instance for signs of compromise such as unexpected commands, unexplained PTY sessions, or modified files.