CVE-2025-30218
CVE-2025-30218 is a Information Exposure vulnerability in next. O3 Security confirms whether CVE-2025-30218 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Next.js may leak x-middleware-subrequest-id to external hosts
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. To mitigate CVE-2025-29927, Next.js validated the x-middleware-subrequest-id which persisted across multiple incoming requests. However, this subrequest ID is sent to all requests, even if the destination is not the same host as the Next.js application. Initiating a fetch request to a third-party within Middleware will send the x-middleware-subrequest-id to that third party. This vulnerability is fixed in 12.3.6, 13.5.10, 14.2.26, and 15.2.4.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | next | ≥ 12.3.5&&< 12.3.6 | 12.3.6 |
| 📦npm | next | ≥ 13.5.9&&< 13.5.10 | 13.5.10 |
| 📦npm | next | ≥ 14.2.25&&< 14.2.26 | 14.2.26 |
| 📦npm | next | ≥ 15.2.3&&< 15.2.4 | 15.2.4 |
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 12.3.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-30218 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-2025-30218 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-2025-30218. 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-2025-30218 in your dependencies?
O3 detects CVE-2025-30218 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.