The vulnerability, tracked as CVE-2026-76461, carries a 9.8 CVSS score and affects physical and virtual Secure Email Gateway appliances regardless of their configuration. Cisco says there are no workarounds, so patching is the only fix.

The bug lies in how Cisco's AsyncOS software handles incoming email. An attacker doesn't need to log in: they can send a booby-trapped message through a vulnerable gateway and, if the exploit works, run commands as root.