[2025 December Notification] ZLD5.41 Firmware Upgrade

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Zyxel_Avani
Zyxel_Avani Posts: 27 image  Zyxel Employee
First Anniversary
edited December 2025 in Security Highlight
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Zyxel is committed to keeping your devices up to date for optimal performance and security. This release includes key maintenance updates and enhancements, such as:

Feature Enhancements and Consolidated Bug fixes

Feature Enhancements

- Improved user experience in Security Best Practices flow.

💡Resolved issues*

Bug ID

Description

241101556

Fix: Edit single-AP configuration. The configuration dialog will keep spinning and cannot load.

250302438

Fix: DNS thread filter function caused clients is unable to get DNS reply from Internet.

250401225

Fix: When session limit is enabled and client session is full, the firewall will stop to use SNAT and forwards traffic to Internet.

250500239

Fix: Unable to preview Billing Profile while Hotspot Management license is still in the Grace Period.

250501605

Fix: Interface cannot be set to 0.0.0.0

250600078

Fix: The ext-group-use AD queries are not working on the backup AD server because the firewall failed to send AD queries to the backup server.

250600445

Fix: AD authentication failure after firmware update to V5.40

250601710

Fix: AP slot configuration not being in order will cause Device-HA synchronization to fail. Device-HA synchronization mechanism will ignore the ordering of AP slot configurations.

250700434

Fix: L2TP PPP connects to "StrongVPN" what will result firewall crash.

250700827

Fix: Managed APs disconnected from controller caused by an issue in the library code implementation.

250700834

Fix: Unexpected communication between VLANs.

250701461

Fix: Sandboxing causes the device to run out of memory.

250701974

Fix: CPU usage may show 99–100% due to an overflow that occurred during calculation, resulting in a display error.

250800640

Fix: External Black List can't update.

*For full details, please refer to the release notes.

👉Upgrade your devices to ZLD5.41 for enhanced protection against the CVE references listed, as ZLD5.41 is no longer vulnerable to them.

Release Date: October 20th, 2025

Supported Models: ATP Series/USG FLEX Series/USG FLEX 50 (USG20-VPN)/USG20W-VPN

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