CVE-2026-27977
CVE-2026-27977 is a CWE-1385 vulnerability in next. O3 Security confirms whether CVE-2026-27977 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Next.js: null origin can bypass dev HMR websocket CSRF checks
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
nextnpmDescription
Next.js is a React framework for building full-stack web applications. Starting in version 16.0.1 and prior to version 16.1.7, in next dev, cross-site protection for internal websocket endpoints could treat Origin: null as a bypass case even if allowedDevOrigins is configured, allowing privacy-sensitive/opaque contexts (for example sandboxed documents) to connect unexpectedly. If a dev server is reachable from attacker-controlled content, an attacker may be able to connect to the HMR websocket channel and interact with dev websocket traffic. This affects development mode only. Apps without a configured allowedDevOrigins still allow connections from any origin. The issue is fixed in version 16.1.7 by validating Origin: null through the same cross-site origin-allowance checks used for other origins. If upgrading is not immediately possible, do not expose next dev to untrusted networks and/or block websocket upgrades to /_next/webpack-hmr when Origin is null at the proxy.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | next | ≥ 16.0.1&&< 16.1.7 | 16.1.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for next. 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 next to 16.1.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27977 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-2026-27977 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-2026-27977. 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-2026-27977 in your dependencies?
O3 detects CVE-2026-27977 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.