CVE-2021-25736 is a medium-severity (CVSS 6.3) CWE-114 vulnerability in k8s.io/kubernetes. O3 Security confirms whether CVE-2021-25736 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Kube-proxy may unintentionally forward traffic
Real-World Exposure
k8s.io/kubernetesReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Kube-proxy on Windows can unintentionally forward traffic to local processes listening on the same port (“spec.ports[*].port”) as a LoadBalancer Service when the LoadBalancer controller does not set the “status.loadBalancer.ingress[].ip” field. Clusters where the LoadBalancer controller sets the “status.loadBalancer.ingress[].ip” field are unaffected.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | k8s.io/kubernetes | all versions | 1.21.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for k8s.io/kubernetes. 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 k8s.io/kubernetes to 1.21.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-25736 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-2021-25736 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-2021-25736. 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-2021-25736 in your dependencies?
O3 detects CVE-2021-25736 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.