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Fencer Vulns
high 7.5

CVE-2021-43803 in the critical feed json

Unexpected server crash in Next.js

published 2021-12-06 4 y ago modified 2026-07-08 4 mo ago also EUVD-2021-2419 , GHSA-25mp-g6fv-mqxx

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
47.3%
EPSS 47.3% chance of exploitation in 30 days, percentile 98%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm next 11.1.3, 12.0.5
  • vercel next.js 11.1.3, 12.0.5

Exploit prediction

47.25% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P

Affected packages

ecosystem package affected fixed in
npm next
>=12.0.0, <12.0.5
>=0.9.9, <11.1.3
12.0.5
11.1.3

Affected products

  • vercel next.js

Classification

Weakness
  • CWE-20 Improper Input Validation
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of vercel/next.js published their own advisory on GitHub. Reviewed sources take precedence over it.