CVE-2021-43801
HIGHCVE-2021-43801 is a high-severity (CVSS 7.5) CWE-754 vulnerability in mercurius. O3 Security confirms whether CVE-2021-43801 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Uncaught Exception in mercurius
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
mercuriusnpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | mercurius | ≥ 8.10.0&&< 8.11.2 | 8.11.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mercurius. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-43801 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-43801. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-43801 in your dependencies?
O3 detects CVE-2021-43801 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.