Zyxel customers are facing reboot loops, high CPU usage, and login issues after an update on Friday went awry. The only fix requires physical access and a Console/RS232 cable, as no remote recovery options are available. The Register reports: "We've found an issue affecting a few devices that may cause reboot loops, ZySH daemon failures, or login access problems," Zyxel's advisory reads. "The system LED may also flash. Please note this is not related to a CVE or security issue." "The issue stems from a failure in the Application Signature Update, not a firmware upgrade. To address this, we've disabled the application signature on our servers, preventing further impact on firewalls that haven't loaded the new signature versions."

The firewalls affected include USG Flex boxes and ATP Series devices running ZLD firmware versions -- installations that have active security licenses and dedicated signature updates enabled in on-premises/standalone mode. Those running on the Nebula platform, on USG Flex H (uOS), and those without valid security licenses are not affected.

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