ASD's Australian Cyber Security Centre warns of active exploitation of CVE-2026-63077 in TeamCity On-Premises servers, a vulnerability that can allow unauthenticated HTTP(S) attackers to bypass authentication and execute arbitrary operating system commands; the alert advises organisations to identify vulnerable TeamCity instances, remove internet exposure where possible, apply vendor patches promptly, monitor for suspicious activity using vendor-provided IoCs, and contact ACSC if compromise is suspected.