# CVE-2021-22161: Denial of service in n/a

> An attacker can trigger a routing loop in OpenWrt devices using IPv6, causing excessive network traffic and potential service disruption.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 7 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-jw75-vvj8-5h3f

## What is CVE-2021-22161?

CVE-2021-22161 is a medium-severity denial of service vulnerability in Openwrt Openwrt, published on 7 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In OpenWrt 19.07.x before 19.07.7, 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. This affects the netifd and odhcp6c packages.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2021-22161?

It affects 1 product.


Products: Openwrt Openwrt.

## How do I fix CVE-2021-22161?

No fix has been published for CVE-2021-22161 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-22161 being exploited?

There is no known exploitation of CVE-2021-22161 in the wild and no public exploit code.

## Other vulnerabilities in Openwrt Openwrt

- [CVE-2020-28951](https://insights.sbomify.com/CVE-2020-28951/): Use after free in n/a (critical 9.8)
- [CVE-2026-62948](https://insights.sbomify.com/CVE-2026-62948/): Cross-site scripting in openwrt (critical 9.6)
- [CVE-2026-30871](https://insights.sbomify.com/CVE-2026-30871/): OpenWrt Project has Stack-based Buffer Overflow in DNS PTR Query (critical 9.5)
- [CVE-2026-30872](https://insights.sbomify.com/CVE-2026-30872/): OpenWrt Project has a Stack-based Buffer Overflow vulnerability via IPv6 reverse DNS lookup (critical 9.5)
- [CVE-2021-28961](https://insights.sbomify.com/CVE-2021-28961/): Command injection in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-22161 and fix it if it is affected.

What it is: CVE-2021-22161 is a medium-severity denial of service vulnerability in Openwrt Openwrt, published on 7 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-22161 in the wild and no public exploit code.

Affected product: Openwrt Openwrt. 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-2021-22161/ (Markdown: https://insights.sbomify.com/CVE-2021-22161/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-22161
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-22161
- OSV: https://osv.dev/vulnerability/CVE-2021-22161

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-22161/
Summaries are generated and may contain mistakes; the official description above is the record.