> Cisco make-me-root email bug exploited as a 0-day by unknown crims

Cisco “strongly” implored customers to patch yet another critical, make-me-root vulnerability in its Secure Email Gateway (SEG), one that has already been exploited in zero-day attacks. A Cisco spokesperson told The Register that the critical vuln, which received a 9.8 out of 10 CVSS rating, affects “a limited number of customers.” The bug, now tracked as CVE‑2026‑76519, allows remote, unauthenticated attackers to write files and execute commands with root privileges on the appliance’s operating system - simply by sending a malicious email. In separate Wednesday advisories, both the networking vendor and the US government warned that attackers were exploiting the latest SEG vulnerability before Cisco issued a fix. The US Cybersecurity and Infrastructure Security Agency (CISA) added the vulnerability to its Known Exploited Vulnerabilities catalog, and set a Saturday deadline for federal agencies to fix the issue. “We are aware of active exploitation of this vulnerability,” the spokesperson said, but declined to answer our questions about how many appliances had been compromised, and what attackers were doing with this access after exploiting the bug. “We strongly urge customers to upgrade to a fixed software release and follow additional recommendations and hardening guidance in our advisory,” the spokesperson said. The flaw exists in SEG’s Advanced Malware Protection (AMP) feature, and it’s due to improper handling of email attachments. An attacker could exploit the bug by sending an email with a malicious attachment, and a successful exploit would allow them to write files and execute commands as root on the compromised appliance. This vulnerability affects both physical and virtual SEG appliances running a vulnerable release of Cisco AsyncOS Software if both of the following conditions are met: The File Reputation service, which is part of Cisco AMP, is enabled and assigned to a mail policy. The Content Scanner Tools version is earlier than 25.3.0.5525. Cisco's Wednesday advisory includes steps organizations can take to determine whether File Reputation is enabled and which Content Scanner Tools version is installed - so give that a read if you are unsure. Upgrading to a fixed Cisco AsyncOS Software release will patch the security hole, and there are no workarounds. The vendor recommends any customers who are running Cisco AsyncOS Software releases earlier than v 16.5 migrate to 16.5.0-780. In its alert, Cisco said it became aware of active exploitation in October. This is the second such zero-day in SEG in as many months. In mid-September, Cisco warned customers that criminals were exploiting a similar bug in SEG, tracked as CVE-2026-76461, that also turns a malicious email into root access. In January, attackers exploited another critical AsyncOS flaw, CVE-2025-20393, to break into Cisco SEG appliances and install persistence mechanisms. That bug eventually scored a perfect 10.®