CVE-2021-3128

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.

Published: 2021-04-12 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3128 is rated Moderate Risk (57.7/100): CVSS High severity, with medium exploitation likelihood (EPSS 2.18%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3128

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 2.48% 2.18% -0.30%
2 2025-04-15 2.33% 2.48% +0.15%
3 2025-03-30 — 2.33% —

Full EPSS history (18 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3128

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-3128

Affected software / configurations for CVE-2021-3128

Vendor Product Version Raw CPE
asus zenwifi_ax_\(xt8\)_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:zenwifi_ax_\(xt8\)_firmware:*:*:*:*:*:*:*:*
asus zenwifi_ax_\(xt8\)_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:zenwifi_ax_\(xt8\)_firmware:*:*:*:*:*:*:*:*
asus rt-ax3000_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax3000_firmware:*:*:*:*:*:*:*:*
asus rt-ax3000_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax3000_firmware:*:*:*:*:*:*:*:*
asus rt-ax55_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax55_firmware:*:*:*:*:*:*:*:*
asus rt-ax55_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax55_firmware:*:*:*:*:*:*:*:*
asus rt-ax56u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax56u_firmware:*:*:*:*:*:*:*:*
asus rt-ax56u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax56u_firmware:*:*:*:*:*:*:*:*
asus rt-ax58u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax58u_firmware:*:*:*:*:*:*:*:*
asus rt-ax58u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax58u_firmware:*:*:*:*:*:*:*:*
asus rt-ax68u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax68u_firmware:*:*:*:*:*:*:*:*
asus rt-ax68u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax68u_firmware:*:*:*:*:*:*:*:*
asus rt-ax82u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax82u_firmware:*:*:*:*:*:*:*:*
asus rt-ax82u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax82u_firmware:*:*:*:*:*:*:*:*
asus rt-ax86u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax86u_firmware:*:*:*:*:*:*:*:*
asus rt-ax86u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax86u_firmware:*:*:*:*:*:*:*:*
asus rt-ax88u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ax88u_firmware:*:*:*:*:*:*:*:*
asus rt-ax88u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ax88u_firmware:*:*:*:*:*:*:*:*
asus rt-ac66u_b1_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac66u_b1_firmware:*:*:*:*:*:*:*:*
asus rt-ac66u_b1_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac66u_b1_firmware:*:*:*:*:*:*:*:*
asus rt-ac1750_b1_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac1750_b1_firmware:*:*:*:*:*:*:*:*
asus rt-ac1750_b1_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac1750_b1_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac1900_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac1900_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900p_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac1900p_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900p_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac1900p_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac1900u_firmware:*:*:*:*:*:*:*:*
asus rt-ac1900u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac1900u_firmware:*:*:*:*:*:*:*:*
asus rt-ac2900_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac2900_firmware:*:*:*:*:*:*:*:*
asus rt-ac2900_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac2900_firmware:*:*:*:*:*:*:*:*
asus rt-ac3100_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac3100_firmware:*:*:*:*:*:*:*:*
asus rt-ac3100_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac3100_firmware:*:*:*:*:*:*:*:*
asus rt-ac5300_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac5300_firmware:*:*:*:*:*:*:*:*
asus rt-ac5300_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac5300_firmware:*:*:*:*:*:*:*:*
asus rt-ac58u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac58u_firmware:*:*:*:*:*:*:*:*
asus rt-ac58u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac58u_firmware:*:*:*:*:*:*:*:*
asus rt-ac65u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac65u_firmware:*:*:*:*:*:*:*:*
asus rt-ac65u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac65u_firmware:*:*:*:*:*:*:*:*
asus rt-ac68p_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac68p_firmware:*:*:*:*:*:*:*:*
asus rt-ac68p_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac68p_firmware:*:*:*:*:*:*:*:*
asus rt-ac68r_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac68r_firmware:*:*:*:*:*:*:*:*
asus rt-ac68r_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac68r_firmware:*:*:*:*:*:*:*:*
asus rt-ac68rw_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac68rw_firmware:*:*:*:*:*:*:*:*
asus rt-ac68rw_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac68rw_firmware:*:*:*:*:*:*:*:*
asus rt-ac68u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac68u_firmware:*:*:*:*:*:*:*:*
asus rt-ac68u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac68u_firmware:*:*:*:*:*:*:*:*
asus rt-ac68w_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac68w_firmware:*:*:*:*:*:*:*:*
asus rt-ac68w_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac68w_firmware:*:*:*:*:*:*:*:*
asus rt-ac85u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac85u_firmware:*:*:*:*:*:*:*:*
asus rt-ac85u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac85u_firmware:*:*:*:*:*:*:*:*
asus rt-ac86u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac86u_firmware:*:*:*:*:*:*:*:*
asus rt-ac86u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac86u_firmware:*:*:*:*:*:*:*:*
asus rt-ac88u_firmware < 3.0.0.4.386.42095 cpe:2.3:o:asus:rt-ac88u_firmware:*:*:*:*:*:*:*:*
asus rt-ac88u_firmware < 9.0.0.4.386.41994 cpe:2.3:o:asus:rt-ac88u_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-3128

URL Tags
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
https://www.asus.com/supportonly/RT-AC68R/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC68RW/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC68U/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC68W/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC85U/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC86U/HelpDesk_download/ Product Vendor Advisory
https://www.asus.com/supportonly/RT-AC88U/HelpDesk_download/ Product Vendor Advisory
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