What is CVE-2021-43803?

CVE-2021-43803 is a high-severity vulnerability in Node.js, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2021-12-10.

How severe is CVE-2021-43803?

High severity. CVSS v3 base score is 7.5 out of 10.

Is CVE-2021-43803 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Improper input validation in Node.js

CVE-2021-43803

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.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2021-12-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.448 (98.7th percentile), scored 2026-09-28.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 99th percentile — 98.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.448 · newest: 0.448 · change: 0.000

Affected products

Node.js
Vercel Next.js — versions >= 11.1.0, < 11.1.3, >= 12.0.0, < 12.0.5

Weakness classification (CWE)

CWE-20 — Improper Input Validation

Public proof-of-concept exploits

References

github.com/vercel/next.js/security/advisories/GHSA-25mp-g6fv-mqxx (Patch, Third Party Advisory)
github.com/vercel/next.js/pull/32080 (Patch, Third Party Advisory)
github.com/vercel/next.js/commit/6d98b4fb4315dec1badecf0e9bdc212a4272b264 (Patch, Third Party Advisory)
github.com/vercel/next.js/releases/tag/v11.1.3 (Third Party Advisory, Release Notes)
github.com/vercel/next.js/releases/v12.0.5 (Third Party Advisory, Release Notes)

Frequently asked questions

What is CVE-2021-43803?: CVE-2021-43803 is a high-severity vulnerability in Node.js, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2021-12-10.
How severe is CVE-2021-43803?: High severity. CVSS v3 base score is 7.5 out of 10.
Is CVE-2021-43803 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.