GHSA-ffhc-5mcf-pf4q
MEDIUMGHSA-ffhc-5mcf-pf4q is a medium-severity (CVSS 4.7) vulnerability in next. O3 Security confirms whether GHSA-ffhc-5mcf-pf4q is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Next.js vulnerable to cross-site scripting in App Router applications using CSP nonces
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
nextnpmDescription
Impact
App Router applications that rely on CSP nonces can be vulnerable to stored cross-site scripting when deployed behind shared caches. In affected versions, malformed nonce values derived from request headers could be reflected into rendered HTML in an unsafe way, allowing an attacker to poison cached responses and cause script execution for later visitors.
Fix
We now reject or ignore malformed nonce values before they are embedded into HTML and apply stricter nonce sanitization so request-derived nonce data cannot break out of the intended attribute context.
Workarounds
If you cannot upgrade immediately, strip inbound Content-Security-Policy request headers from untrusted traffic.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | next | ≥ 13.4.0&&< 15.5.16 | 15.5.16 |
| 📦npm | next | ≥ 16.0.0&&< 16.2.5 | 16.2.5 |
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 15.5.16 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-ffhc-5mcf-pf4q 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 GHSA-ffhc-5mcf-pf4q 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 GHSA-ffhc-5mcf-pf4q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-ffhc-5mcf-pf4q in your dependencies?
O3 detects GHSA-ffhc-5mcf-pf4q across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.