CVE-2021-43801: Mercurius Project Mercurius

High severity, CVSS 7.5. EPSS: 1.6% chance of exploitation in the next 30 days.

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.

Affected products

• Mercurius Project Mercurius: from 8.10.0, before 8.11.2 (fixed in 8.11.2)

Published 2021-12-13. Last modified 2026-06-17.