Notice #248637

ZyXEL Firewall Malware Attack Mitigation and Prevention


ESI Statement on Recent ZyXEL Patch 5.36 ABAR1

ESI is aware of a recent patch developed by ZyXEL that mitigates a malware attack against the Virtual Private Network (VPN) services utilized on ZyXEL devices.

The attack in question locks up the firewall so that administrative access and network traffic are hindered and, in some cases, completely blocked.

As ESI offers the USG20W-VPN (renamed FLEX 50W) as an option. This notification is being sent out to urge customers with those devices to upgrade to the latest firmware (5.36 ABAR1) immediately.

The following is a link to the notice from ZyXEL on their community page:

If help is needed to perform this upgrade, please contact ESI Technical Support to arrange a time to work with a network technician via one of the following: Technical Support phone number: 972-422-9700 Technical Support email:

  • ESI eCloud Hosted PBX
    • ESI ePhoneGO2

      ESI Cloud's mobile solution for iOS and Android

    • SIP Phones

      ESI & 3rd Party phones using eCloud services.

    • ESI ePhone7 Services

      ESI's Android-based desktop phone.

    • ESI eCloud Internet Fax
    • ESI eConsole Dashboard

      Web-based portal to manage users, DIDs, queues, and more.

    • ESI eTeams Connector
    • eCloud Click-to-Call

      Click-to-Call Google Chrome Extension

    • SMS Texting
    • ESI Webphone

      Softphone for eCloud.

  • EsiQuote2

    Sales quote tool for eCloud and eSIP PBX.

  • ESI SIP Trunks
    • Inbound PSTN Carriers
    • Outbound PSTN Carriers
  • ESI Technical Support Portal

    ESI's customer service ticketing system.

  • ESI Academy

    ESI Partner site for training, documentation, community forums.

  • ESI Access Dashboard

    Services associated with the Access Dashboard. This would not affect the firmware of the actual access devices.

Previous Incidents
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