Windows kube-proxy LoadBalancer contention
Priority LOW 30CWE-114Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- High
- Impact type
- —
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00915 60th percentileScored 2026-11-07
Fix Fixed k8s.io/kubernetes (Go): 1.21.0Red Hat: 1 advisory
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Kubernetes | Kubernetes | up to v1.20.5 | — | No fix listed | CNA |
| — | k8s.io/kubernetes (Go) | before 1.21.0 | 1.21.0 | Patch available | GHSA-35c7-w35f-xwgh |
- Kubernetes VendorKubernetes Affected up to v1.20.5 Fixed in — No fix listed CNA
- k8s.io/kubernetes (Go) Vendor— Affected before 1.21.0 Fixed in 1.21.0 Patch available GHSA-35c7-w35f-xwgh
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:kubernetes:kubernetes:*:*:*:*:*:*:*:* | 1.18.0 to before 1.18.18; 1.19.0 to before 1.19.10; 1.20.0 to before 1.20.6 | Vulnerable | Kubernetes |
| cpe:2.3:o:microsoft:windows:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Microsoft |
- cpe:2.3:a:kubernetes:kubernetes:*:*:*:*:*:*:*:* Versions 1.18.0 to before 1.18.18; 1.19.0 to before 1.19.10; 1.20.0 to before 1.20.6 Vulnerable ·Kubernetes
- cpe:2.3:o:microsoft:windows:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Microsoft
Remediation
- Fix · GHSA-35c7-w35f-xwgh k8s.io/kubernetes (Go) Fixed in 1.21.0 Advisory →
Red Hat 1 advisory
- RHSA-2021:2130 Released 2021-06-23 · Red Hat rating ModerateWindows Container Support for Red Hat OpenShift 2.0.1 security and bug fix update
- Red Hat OpenShift Container Platform 4.7 openshift4-wincw/windows-machine-config-operator-bundle, openshift4-wincw/windows-machine-config-rhel8-operator
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat OpenShift Container Platform 4.7 | Fixed | RHSA-2021:2130 |
Timeline
- 2026-10-02 Threatist record created from CVE-2021-25736
- 2026-10-03 Alias added: GHSA-35c7-w35f-xwgh
References
Advisory 3
More Kubernetes vulnerabilities
- TI-2018-16130 Improper privilege management in Kubernetes CVSS 3.0CRITICAL 9.8
- TI-2019-08418 Kubernetes kubelet exposes /debug/pprof info on healthz port CVSS 3.1HIGH 8.2
- TI-2023-05086 Kubernetes - Windows nodes - Insufficient input sanitization in in-tree storage plugin leads to privilege escalation CVSS 3.1HIGH 8.8
- TI-2023-03433 Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation CVSS 3.1HIGH 8.8
- TI-2023-02285 Bypass of seccomp profile enforcement CVSS 3.1MEDIUM 5.5
- TI-2017-14755 Link following in Kubernetes CVSS 3.0CRITICAL 9.6
Sources
- CVE-2021-25736 · CVE Program
- CVE-2021-25736 · NVD
- FIRST EPSS
- GHSA-35c7-w35f-xwgh · GitHub Advisory Database · CC BY 4.0
- CVE-2021-25736 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences