What is CVE-2021-43801?

CVE-2021-43801 is a high-severity vulnerability in Mercurius-Js Mercurius, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 7.5/10. Published 2021-12-13.

How severe is CVE-2021-43801?

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

Vulnerability in Mercurius-Js Mercurius

CVE-2021-43801

Mercurius is a GraphQL adapter for Fastify. Any users from Mercurius@8.10.0 to 8.11.1 are subjected to a denial of service attack by sending a malformed JSON to `/graphql` unless they are using a custom error handler. The vulnerability has been fixed in https://github.com/mercurius-js/mercurius/pull/678 and shipped as v8.11.2. As a workaround users may use a custom error handler.

Published 2021-12-13 · 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: 0.015 (73.6th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 74th percentile — 73.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.015 · newest: 0.015 · change: 0.000

Affected products

Mercurius-Js Mercurius — versions >= 8.10.0, < 8.11.2
Mercurius Project

Weakness classification (CWE)

CWE-754 — Improper Check for Unusual or Exceptional Conditions

References

github.com/mercurius-js/mercurius/security/advisories/GHSA-273r-rm8g-7f3x (Patch, Third Party Advisory)
github.com/mercurius-js/mercurius/issues/677 (Patch, Third Party Advisory, Issue Tracking)
github.com/mercurius-js/mercurius/pull/678/commits/732b2f895312da8deadd7b173dcd… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-43801?: CVE-2021-43801 is a high-severity vulnerability in Mercurius-Js Mercurius, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 7.5/10. Published 2021-12-13.
How severe is CVE-2021-43801?: High severity. CVSS v3 base score is 7.5 out of 10.