HOME VULNERABILITIESCVE-2021-3128

HIGH

CVE-2021-3128

CWE-834Published: April 12, 2021· Updated: Jun 17, 2026

7.5

CVSS v3.1

Official 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.

Technical Analysis

CVE-2021-3128 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges Req.None

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Affected Vendors & Products

asus54 product(s)

zenwifi ax \(xt8\) firmwarezenwifi ax \(xt8\)rt-ax3000 firmwarert-ax3000rt-ax55 firmwarert-ax55rt-ax56u firmwarert-ax56urt-ax58u firmwarert-ax58urt-ax68u firmwarert-ax68u+42

Source: NVD CPE · 54 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time

Offensive Security exploit database

GitHub PoC Search

Community PoC repositories

Rapid7 / Metasploit

Metasploit module search

Security advisories & exploits

Official NIST entry

CVE Program entry

External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/Whole-Home-Mesh-WiFi-System/ZenWiFi-WiFi-Systems/ASUS-ZenWiFi-AX-XT8-/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX3000/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX55/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX56U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX58U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX68U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX82U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX86U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX88U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AC66U-B1/HelpDesk_Download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1750_B1/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900P/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC2900/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC3100/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC5300/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC58U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC65U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68P/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68R/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68RW/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68W/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC85U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC86U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC88U/HelpDesk_download/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/Whole-Home-Mesh-WiFi-System/ZenWiFi-WiFi-Systems/ASUS-ZenWiFi-AX-XT8-/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX3000/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX55/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX56U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX58U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX68U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX82U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX86U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-6/All-series/RT-AX88U/HelpDesk_BIOS/

ADVISORYhttps://www.asus.com/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AC66U-B1/HelpDesk_Download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1750_B1/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900P/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC1900U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC2900/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC3100/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC5300/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC58U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC65U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68P/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68R/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68RW/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC68W/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC85U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC86U/HelpDesk_download/

ADVISORYhttps://www.asus.com/supportonly/RT-AC88U/HelpDesk_download/

All References (54)

→

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

Quick Facts

CVE IDCVE-2021-3128

CVSS Score7.5 / 10

SeverityHIGH

WeaknessCWE-834

CISA KEVNo

Affected1 vendor(s)

PublishedApr 12, 2021

Related CVEs (CWE-834)

Recommended Actions

→Apply vendor patches immediately
→Monitor CVE-2021-3128 in threat intel feeds
→Review IDS/IPS signatures for exploitation attempts

Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.

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