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Vulnerability record · CVE-2021-3128 · published 12 April 2021

CVE-2021-3128: Asus zenwifi ax \(xt8\) firmware vulnerability

Asus · Zenwifi Ax \(Xt8\) Firmware

In ASUS RT-AX3000, ZenWiFi AX (XT8), RT-AX88U, and other ASUS routers with firmware < 3.0.0.4.386.42095 or < 9.0.0.4.386.41994, when IPv6 is used, a routing loop can occur that generates excessive network traffic between an affected device and its upstream ISP's router. This occurs when a link prefix route points to a point-to-point link, a destination IPv6 address belongs to the prefix and is not a local IPv6 address, and a router advertisement is received with at least one global unique IPv6 prefix for which the on-link flag is set.

7.5 CVSS 3.1 High EPSS 2.2% · top 18.3% CWE-834 · CWE-834
7.5CVSS 3.1 base score, v2 5.0
2.2%EPSS exploitation probability, 30 days
NoNot in CISA KEV
27Affected product versions listed by NVD
54References
17 Jun 2026Last modified by NVD

Description

In ASUS RT-AX3000, ZenWiFi AX (XT8), RT-AX88U, and other ASUS routers with firmware < 3.0.0.4.386.42095 or < 9.0.0.4.386.41994, when IPv6 is used, a routing loop can occur that generates excessive network traffic between an affected device and its upstream ISP's router. This occurs when a link prefix route points to a point-to-point link, a destination IPv6 address belongs to the prefix and is not a local IPv6 address, and a router advertisement is received with at least one global unique IPv6 prefix for which the on-link flag is set.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

27 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://www.asus.com/Networking-IoT-Servers/Whole-Home-Mesh-WiFi-System/ZenWiFi-WiFi-Systems/ASUS-ZenWiFi-AX-XT8-/HelpDe ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX3000/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX55/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX56U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX58U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX68U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX82U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX86U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX88U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AC66U-B1/HelpDesk_Download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1750_B1/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1900/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1900P/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1900U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC2900/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC3100/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC5300/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC58U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC65U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC68P/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC68R/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC68RW/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC68U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC68W/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC85U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC86U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC88U/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/Whole-Home-Mesh-WiFi-System/ZenWiFi-WiFi-Systems/ASUS-ZenWiFi-AX-XT8-/HelpDe ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX3000/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX55/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX56U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX58U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX68U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX82U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX86U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX88U/HelpDesk_BIOS/ ProductVendor Advisory
https://www.asus.com/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AC66U-B1/HelpDesk_Download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1750_B1/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1900/HelpDesk_download/ ProductVendor Advisory
https://www.asus.com/supportonly/RT-AC1900P/HelpDesk_download/ ProductVendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-3128), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.