ATP100 – critical regression after upgrade to firmware 5.42(ABPS.0), reboots caused by kern

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Tibor_SK
Tibor_SK Posts: 3 image  Freshman Member
First Comment
in Security

Dear Zyxel Support Team,

I would like to report a critical stability issue affecting a Zyxel ATP100, which started immediately after upgrading to the newly released firmware version 5.42(ABPS.0).

Device: Zyxel ATP100

Firmware: 5.42(ABPS.0) (officially released on 2026-02-04)

Status before upgrade: stable operation on previous firmware (5.41)

Problem description

After upgrading to firmware 5.42(ABPS.0), the device starts rebooting periodically. This is not a manual reboot or power-related issue, but a watchdog-triggered reboot caused by a kernel soft lockup.

Crash logs consistently show:

BUG: soft lockup - CPU#1 stuck for 31s! [fqdnobjectd]

The call trace repeatedly points to the fqdn_object kernel module and the fqdnobjectd process, specifically the function:

fqdnObject_syncQ_chrdev_sync()

This strongly indicates a deadlock or infinite wait condition in the FQDN (DNS/domain handling) subsystem, which eventually causes the watchdog to reboot the system.

  • The issue started immediately after the upgrade to 5.42
  • No configuration changes were made
  • The behavior clearly indicates a regression bug in firmware 5.42, as the same configuration was stable on 5.41

I can provide full crash logs if needed.

Thanks.

Accepted Solution

All Replies

  • Zyxel_Melen
    Zyxel_Melen Posts: 4,533 image  Zyxel Employee
    Zyxel Certified Network Engineer Level 1 - Switch Zyxel Certified Network Administrator - Switch Zyxel Certified Network Administrator - Nebula Zyxel Certified Sales Associate
    Answer ✓

    Hi @Tibor_SK

    I will send you a private message for the full crash logs. Please also help to collect:

    1. Device configuration "start-up config".
    2. Device diagnostic file.
    https://community.zyxel.com/en/discussion/26074/atp-flex-how-to-collect-diagnostic-file-on-firewall-local-web-gui
    Zyxel Melen


  • Zyxel_Cooldia
    Zyxel_Cooldia Posts: 1,570 image  Zyxel Employee
    Zyxel Certified Network Administrator - Security Zyxel Certified Sales Associate 100 Answers 1000 Comments
    edited February 6

    Hi @Tibor_SK,

    To avoid service impact, you can switch the firmware partition by going to “MAINTENANCE > File Manager > Firmware Management”
    We are checking this issue and will keep the community updated on the status.

    Web GUI:

    image.png

    CLI:

    https://community.zyxel.com/en/discussion/25856

  • Tibor_SK
    Tibor_SK Posts: 3 image  Freshman Member
    First Comment

    Dear Support Team,

    the requested diagnostic data have been provided. As a temporary mitigation, I have switched the device firmware back to version 5.41, which is currently operating stably.

    Please let me know if any further information or testing is required.

    Kind regards.

  • Zyxel_Vic
    Zyxel_Vic Posts: 323 image  Zyxel Employee
    25 Answers First Comment Friend Collector Eighth Anniversary

    Hi @Tibor_SK

    We sincerely apologize for your inconvenience in certain issue and thanks for your assistance so that we're able to address the root cause in short time. Here we have a firmware which fixed the issue you met.

    https://1drv.ms/u/c/a33c4d75c38ddf7d/IQC97Mb7BrkdRq4B1Ww2v5xKAdnuh-bxrB6PpDJWOQgXKGc?e=oPQ3sw

  • alexey
    alexey Posts: 193 image  Master Member
    First Comment Friend Collector Eighth Anniversary
    https://community.zyxel.com/en/discussion/comment/83422#Comment_83422

    Great speed. When we can download FW for other series (ATP800 https://community.zyxel.com/en/discussion/32317/atp800-kernel-panic-fqdnobject-syncq-chrdev-sync#latest)?

  • Zyxel_Vic
    Zyxel_Vic Posts: 323 image  Zyxel Employee
    25 Answers First Comment Friend Collector Eighth Anniversary
    edited February 7

    Hi @alexey

    Thanks for asking. Since we had received several upgrading failure cases recently, we decide to release a patch firmware for all ATP/FLEX Series soon. The schedule will be on next Wed. Apologized for the inconvenience and thanks for your patience.

  • alexey
    alexey Posts: 193 image  Master Member
    First Comment Friend Collector Eighth Anniversary
    https://community.zyxel.com/en/discussion/comment/83425#Comment_83425

    Sorry, but its too long. Our company have 15 min downtime every few hours, because ATP rebooting.

    You know reason, you already give patched FW. What a problem build new FW for another device?

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