Critical WatchGuard Fireware Vulnerability Actively Exploited

A critical out-of-bounds write vulnerability, tracked as CVE-2025-9242, has been discovered in WatchGuard Fireware OS, affecting versions 11.10.2 through 11.12.4_Update1, 12.0 through 12.11.3, and 2025.1. This flaw allows remote, unauthenticated attackers to execute arbitrary code on vulnerable Firebox firewall devices by exploiting a missing length check during the IKE handshake process. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog following evidence of active exploitation, and has mandated that Federal Civilian Executive Branch (FCEB) agencies apply patches by December 3, 2025. As of mid-November, over 54,000 Firebox devices remain exposed globally, with the highest concentrations in the U.S., Italy, the U.K., Germany, and Canada.

WatchGuard released patches for the vulnerability on September 17, 2025, but only confirmed active exploitation in late October. CISA has emphasized the significant risk posed by this flaw, urging all organizations—not just federal agencies—to prioritize patching due to the attractiveness of firewall devices as targets for threat actors. The vulnerability's exploitation path allows attackers to bypass authentication, as the vulnerable code is executed before certificate validation. Organizations unable to apply mitigations are advised to discontinue use of affected products to prevent compromise.