Cisco Warns of Active Exploitation of Critical Secure Email Gateway Vulnerability (CVE-2026-76519)

Cisco has issued an advisory regarding a critical vulnerability (CVE-2026-76519, CVSS score: 9.8) in its Secure Email Gateway that is actively being exploited. The flaw allows an unauthenticated attacker to write files to the appliance's operating system by sending an email with a crafted attachment, potentially leading to root command execution. The vulnerability affects gateways with the File Reputation service enabled and a Content Scanner Tools package older than version 25.3.0.5525. Fixes have been available since September 14, 2026, in AsyncOS 15.5.5-014 and 16.5.0-780, and via a Content Scanner Tools update.