CVE-2025-7339
LOWCVE-2025-7339 is a low-severity (CVSS 3.4) CWE-241 vulnerability in on-headers. O3 Security confirms whether CVE-2025-7339 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
on-headers vulnerable to http response header manipulation
Blast Radius
on-headersReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
on-headers is a node.js middleware for listening to when a response writes headers. A bug in on-headers versions <1.1.0 may result in response headers being inadvertently modified when an array is passed to response.writeHead(). Users should upgrade to version 1.1.0 to receive a patch. Uses are strongly encouraged to upgrade to 1.1.0, but this issue can be worked around by passing an object to response.writeHead() rather than an array.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | on-headers | all versions | 1.1.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for on-headers. 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 on-headers to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-7339 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-2025-7339 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-2025-7339. 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-2025-7339 in your dependencies?
O3 detects CVE-2025-7339 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.