CVE-2021-25736
Windows kube-proxy LoadBalancer contention
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- High
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Windows kube-proxy LoadBalancer contention
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.
- Record
CVE-2021-25736- CVSS 3.1
- 5.8 Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-114
- Updated
- 2026-11-02
EUVDEUVD-2023-2624
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.
- Record
EUVD-2023-2624- CVSS 3.1
- 5.8 Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-35c7-w35f-xwgh
Kube-proxy may unintentionally forward traffic
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.
- Record
GHSA-35c7-w35f-xwgh- CVSS 3.1
- 5.8 Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-02
NVD
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.
- Record
CVE-2021-25736- CVSS 3.1
- 5.8 Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N - CVSS 3.1
- 6.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-114
- Updated
- 2026-11-02
OSV
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.
- Record
CVE-2021-25736- CVSS 3.1
- 6.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-02
OSVGHSA-35c7-w35f-xwgh
Kube-proxy may unintentionally forward traffic
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.
- Record
GHSA-35c7-w35f-xwgh- CVSS 3.1
- 5.8 Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-02
OSVGO-2023-2159 No score
Kube-proxy may unintentionally forward traffic in k8s.io/kubernetes
Kube-proxy may unintentionally forward traffic in k8s.io/kubernetes
- Record
GO-2023-2159- Updated
- 2026-11-02
OSVopenSUSE-SU-2025:15424-1 No score
govulncheck-vulndb-0.0.20250807T150727-1.1 on GA media
These are all security issues fixed in the govulncheck-vulndb-0.0.20250807T150727-1.1 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2025:15424-1- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
k8s.io/kubernetesGo |
before 1.21.0 | 1.21.0 |
govulncheck-vulndbopenSUSE:Tumbleweed From an advisory covering 44 CVEs |
before 0.0.20250807T150727-1.1 | 0.0.20250807T150727-1.1 |
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | ||
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-25736 is a medium vulnerability (CVSS 5.8) in Kubernetes, published October 30, 2023. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.92%, the 60th percentile. Fixed in k8s.io/kubernetes 1.21.0.
References
github.com/kubernetes/kubernetes/pull/99958
groups.google.com/g/kubernetes-security-announce/c/lIoOPObO51Q/m/O15LOazPAgAJ
security.netapp.com/advisory/ntap-20231221-0003
nvd.nist.gov/vuln/detail/CVE-2021-25736
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suse.com/security/cve/CVE-2015-7561