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.

Published: 2023-10-30 Last update: 2025-06-12 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-25736 is rated Low Risk (33.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.12%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-25736

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-11-21 0.27% 0.12% -0.15%
2 2025-11-18 0.12% 0.27% +0.15%
3 2025-03-30 — 0.12% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-25736

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.8 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.3 4.0 [email protected]
6.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.8 4.0 [email protected]

Weakness enumeration for CVE-2021-25736

GitHub Security Advisory for CVE-2021-25736

GHSA-35c7-w35f-xwgh · Severity: medium · Ecosystem: go — Kube-proxy may unintentionally forward traffic

OS Trackers for CVE-2021-25736

vendor priority summary link
debian unimportant CVE-2021-25736 unimportant priority: Debian including 1 source packages (kubernetes), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-25736
redhat medium — https://access.redhat.com/security/cve/CVE-2021-25736
ubuntu medium CVE-2021-25736 medium priority: Ubuntu including 1 source packages (kubernetes), 7 status rows across 7 suites (bionic, focal, groovy, hirsute, trusty, upstream, xenial): not-affected 4, DNE 3. https://ubuntu.com/security/CVE-2021-25736

Affected software / configurations for CVE-2021-25736

Vendor Product Version Raw CPE
kubernetes kubernetes >= 1.18.0, < 1.18.18 cpe:2.3:a:kubernetes:kubernetes:*:*:*:*:*:*:*:*
kubernetes kubernetes >= 1.19.0, < 1.19.10 cpe:2.3:a:kubernetes:kubernetes:*:*:*:*:*:*:*:*
kubernetes kubernetes >= 1.20.0, < 1.20.6 cpe:2.3:a:kubernetes:kubernetes:*:*:*:*:*:*:*:*

References for CVE-2021-25736

cvelogic Threat Intelligence