CVE-2026-40879
HIGHCVE-2026-40879 is a high-severity (CVSS 7.5) CWE-674 vulnerability in @nestjs/microservices. O3 Security confirms whether CVE-2026-40879 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Nest: DoS via Recursive handleData in JsonSocket (TCP Transport)
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@nestjs/microservicesnpmDescription
Nest is a framework for building scalable Node.js server-side applications. Prior to 11.1.19, when an attacker sends many small, valid JSON messages in one TCP frame, handleData() recurses once per message; the buffer shrinks each call. maxBufferSize is never reached; call stack overflows instead. A ~47 KB payload is sufficient to trigger RangeError. This vulnerability is fixed in 11.1.19.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @nestjs/microservices | all versions | 11.1.19 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @nestjs/microservices. 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 @nestjs/microservices to 11.1.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40879 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-2026-40879 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-2026-40879. 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-2026-40879 in your dependencies?
O3 detects CVE-2026-40879 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.