CVEs / CVE-2021-3128
CVE-2021-3128: n/a n/a vulnerability
- high 7.5 CVSS 3.1 (NVD)
- EPSS 16.1% chance of exploitation in the next 30 days, higher than 96% of CVEs (1 Nov 2026)
- Last changed at its sources
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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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| n/a n/a | n/a | — |
Exploitation
Not in the CISA Known Exploited Vulnerabilities catalog as of 30 Oct 2026.
Severity
| CVSS 3.1 | 7.5 highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HScored by NVD |
|---|---|
| Weakness | CWE-834 |
References
- CVE-2021-3128 on NVD
- https://www.asus.com/Networking-IoT-Servers/Whole-Home-Mesh-WiFi-System/ZenWiFi-WiFi-Systems/ASUS-ZenWiFi-AX-XT8-/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX3000/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX55/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX56U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX58U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX68U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX82U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX86U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX88U/HelpDesk_BIOS/ Product, Vendor Advisory
- https://www.asus.com/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AC66U-B1/HelpDesk_Download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC1750_B1/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC1900/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC1900P/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC1900U/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC2900/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC3100/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC5300/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC58U/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC65U/HelpDesk_download/ Product, Vendor Advisory
- https://www.asus.com/supportonly/RT-AC68P/HelpDesk_download/ Product, Vendor Advisory
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.