How severe is CVE-2021-43801?

CVE-2021-43801 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-43801?

CVE-2021-43801 affects the following packages: mercurius (npm). Ecosystems affected: npm.

How do I fix CVE-2021-43801?

Update mercurius to 8.11.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43801 is resolved across your whole dependency graph.

How do I detect CVE-2021-43801 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mercurius, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-43801 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-43801 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-43801 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-43801?

CVE-2021-43801 has an EPSS (Exploit Prediction Scoring System) score of 1.6%, placing it in the 76th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-43801?

CVE-2021-43801 is classified as CWE-754 (CWE-754). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-43801 published, and has it been updated?

CVE-2021-43801 was published on December 13, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

CVE-2021-43801 — mercurius

HIGHFix: mercurius-js/mercurius#678

CVE-2021-43801 is a high-severity (CVSS 7.5) CWE-754 vulnerability in mercurius. A fix is available for mercurius — see the affected versions and patch details below.

Uncaught Exception in mercurius

Also known asGHSA-273r-rm8g-7f3x

Published

Dec 13, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs76th percentile — riskier than 76% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

91other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

mercuriusnpm

341Kdownloads / week

Description

Impact

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.

Patches

The vulnerability has been fixed in https://github.com/mercurius-js/mercurius/pull/678 and shipped as v8.11.2.

Workarounds

Use a custom error handler.

References

See https://github.com/mercurius-js/mercurius/issues/677

For more information

If you have any questions or comments about this advisory:

Open an issue in https://github.com/mercurius-js/mercurius
Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`mercurius`	≥ 8.10.0&&< 8.11.2	8.11.2`npm install mercurius@8.11.2`

Affected Products

1 product · 1 configurations

Application

mercuriusmercurius_project

≥ 8.10.0 && < 8.11.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mercurius, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mercurius to 8.11.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43801 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Impact 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. ### Patches The vulnerability has been fixed in https://github.com/mercurius-js/mercurius/pull/678 and shipped as v8.11.2. ### Workarounds Use a custom error handler. ### References See https://github.com/mercurius-js/mercurius/issues/677 ### For more information If you have any questions or comments about this advisory: * Open an issue in https://github.com/mercurius-js/mercurius * Email us at [hello@ma