# CVE-2022-21721: DOS Vulnerability in next.js

> Attackers can cause denial of service in Next.js applications using built-in i18n support via custom servers, requiring an upgrade to mitigate.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/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:** Yes
- **Published:** 28 Jan 2022
- **Updated:** 5 May 2025
- **Also known as:** GHSA-wr66-vrwm-5g5x

## What is CVE-2022-21721?

CVE-2022-21721 is a medium-severity denial of service vulnerability in Vercel Next.js, published on 28 Jan 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Next.js is a React framework. Starting with version 12.0.0 and prior to version 12.0.9, vulnerable code could allow a bad actor to trigger a denial of service attack for anyone using i18n functionality. In order to be affected by this CVE, one must use next start or a custom server and the built-in i18n support. Deployments on Vercel, along with similar environments where invalid requests are filtered before reaching Next.js, are not affected. A patch has been released, `next@12.0.9`, that mitigates this issue. As a workaround, one may ensure `/${locale}/_next/` is blocked from reaching the Next.js instance until it becomes feasible to upgrade.

## Which versions are affected by CVE-2022-21721?

2 open source packages ship an affected version, including next. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `next` | npm | From 12.0.0 | 12.0.9 |
| `next` | npm | From 12.0.0 | 12.0.9 |

Products: Vercel Next.js.

## How do I fix CVE-2022-21721?

Upgrade next to 12.0.9 or later.

## Is CVE-2022-21721 being exploited?

There is no known exploitation of CVE-2022-21721 in the wild and no public exploit code.

## Other vulnerabilities in Vercel Next.js

- [CVE-2025-29927](https://insights.sbomify.com/CVE-2025-29927/): Authorization Bypass in Next.js Middleware (critical 9.1)
- [CVE-2026-44578](https://insights.sbomify.com/CVE-2026-44578/): Next.js: Server-side request forgery in applications using WebSocket upgrades (high 8.6)
- [CVE-2026-94483](https://insights.sbomify.com/CVE-2026-94483/): Next.js: Server-Side Request Forgery in Image Optimization (high 8.3)
- [CVE-2026-64642](https://insights.sbomify.com/CVE-2026-64642/): Next.js: Middleware / Proxy bypass in App Router applications using Turbopack and single locale (high 8.3)
- [CVE-2026-64645](https://insights.sbomify.com/CVE-2026-64645/): Next.js: Server-Side Request Forgery in rewrites via attacker-controlled destination hostname (high 8.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-21721 and fix it if it is affected.

What it is: CVE-2022-21721 is a medium-severity denial of service vulnerability in Vercel Next.js, published on 28 Jan 2022. 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-2022-21721 in the wild and no public exploit code.

Affected packages and fixed versions:
- next (npm): affected from 12.0.0; fixed in 12.0.9
- next (npm): affected from 12.0.0; fixed in 12.0.9

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-2022-21721/ (Markdown: https://insights.sbomify.com/CVE-2022-21721/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-21721
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-21721
- OSV: https://osv.dev/vulnerability/CVE-2022-21721

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-21721/
Summaries are generated and may contain mistakes; the official description above is the record.