CVE-2021-25736Network attack vector

Local service exposure via empty ingress IP

Published Oct 30, 2023 · Updated Jun 12, 2025

Information disclosure in Kubernetes kube-proxy 1.20.5 and earlier allows remote authenticated users to access local Windows services. The Windows proxier treats an empty LoadBalancer ingress IP as a valid address and installs an invalid HNS policy that redirects the service port to a same-port local listener. Exposure requires a Windows node, an unset status.loadBalancer.ingress[].ip field, and a local listener on the service port; populated ingress IPs are unaffected.

CVSS severity5.8
Medium
EPSS probability0.92%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Kubernetes kube-proxy 1.20.5 and earlier allows remote authenticated users to access local Windows services. The Windows proxier treats an empty LoadBalancer ingress IP as a valid address and installs an invalid HNS policy that redirects the service port to a same-port local listener. Exposure requires a Windows node, an unset status.loadBalancer.ingress[].ip field, and a local listener on the service port; populated ingress IPs are unaffected.

The record

CVE
CVE-2021-25736
Published
Oct 30, 2023
Updated
Jun 12, 2025
Vendor
Kubernetes
Product
Kubernetes
Classifications
CWE-114
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Oct 30, 2023CVE publishedPublication date reported by the CVE source.
  2. Jun 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=v1.20.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Kubernetes · Kubernetesversion=0 <=v1.20.5

Published CVSS scores

5.8KubernetesCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N
6.3NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-114Process Control

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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