# CVE-2021-3128: Denial of service in n/a

> Attackers can trigger routing loops in ASUS routers using IPv6, causing excessive network traffic and potential service disruption.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-289v-jmv7-6xmx

## What is CVE-2021-3128?

CVE-2021-3128 is a high-severity denial of service vulnerability in n/a, published on 12 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-834 (Excessive Iteration)

## Which versions are affected by CVE-2021-3128?

It affects 27 products.


Products: Asus Rt-Ac1750 B1 Firmware, Asus Rt-Ac1900 Firmware, Asus Rt-Ac1900p Firmware, Asus Rt-Ac1900u Firmware, Asus Rt-Ac2900 Firmware, Asus Rt-Ac3100 Firmware, Asus Rt-Ac5300 Firmware, Asus Rt-Ac58u Firmware, Asus Rt-Ac65u Firmware, Asus Rt-Ac66u B1 Firmware, Asus Rt-Ac68p Firmware, Asus Rt-Ac68r Firmware, Asus Rt-Ac68rw Firmware, Asus Rt-Ac68u Firmware, Asus Rt-Ac68w Firmware, Asus Rt-Ac85u Firmware, Asus Rt-Ac86u Firmware, Asus Rt-Ac88u Firmware, Asus Rt-Ax3000 Firmware, Asus Rt-Ax55 Firmware and 7 more.

## How do I fix CVE-2021-3128?

No fix has been published for CVE-2021-3128 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3128 being exploited?

There is no known exploitation of CVE-2021-3128 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3128 and fix it if it is affected.

What it is: CVE-2021-3128 is a high-severity denial of service vulnerability in n/a, published on 12 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3128 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-3128/ (Markdown: https://insights.sbomify.com/CVE-2021-3128/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3128
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3128
- OSV: https://osv.dev/vulnerability/CVE-2021-3128

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3128/
Summaries are generated and may contain mistakes; the official description above is the record.