How severe is CVE-2021-43801?

CVE-2021-43801 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-43801 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (72nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43801?

CVE-2021-43801 affects Mercurius Project Mercurius. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-43801?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-43801 published?

CVE-2021-43801 was published on 2021-12-13 and last updated on 2026-06-17.

CVE-2021-43801

Q: What is 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.

CVE-2021-43801 is a high-severity vulnerability in Mercurius Project Mercurius with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-754.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (72nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-754
Affected product: Mercurius Project Mercurius
Published: 2021-12-13
Last modified: 2026-06-17

Description

Mercurius is a GraphQL adapter for Fastify. Any users from [email protected] 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.

Frequently asked questions

What is CVE-2021-43801?: Mercurius is a GraphQL adapter for Fastify. Any users from [email protected] 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.
How severe is CVE-2021-43801?: CVE-2021-43801 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-43801 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (72nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43801?: CVE-2021-43801 affects Mercurius Project Mercurius. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-43801?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-43801 published?: CVE-2021-43801 was published on 2021-12-13 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mercurius_project:mercurius:*:*:*:*:*:node.js:*:*

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