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Public proof of conceptFix available

CVE-2021-25735

A public proof of concept exists; no exploitation attested.

  • Published2021-09-06
  • Fixed in1.20.6 · 1.19.10 · 1.18.18
  • WeaknessCWE-372

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A security issue was discovered in kube-apiserver that could allow node updates to bypass a Validating Admission Webhook. Clusters are only affected by this vulnerability if they run a Validating Admission Webhook for Nodes that denies admission based at least partially on the old state of the Node object. Validating Admission Webhook does not observe some previous fields.

Timeline

dates in UTC
  1. 2021-09-0612:15CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-25735?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-25735?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Kubernetes
BranchAffectedFixed in
1.20≥ 1.20.0, < 1.20.61.20.6
1.19≥ 1.19.0, < 1.19.101.19.10
1.18< 1.18.181.18.18

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Kubernetes to 1.20.6 · 1.19.10 · 1.18.18

Advisories and patches

Detection

read 2026-10-23 19:23 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifieddarryk10/CVE-2021-25735
PoC-in-GitHub

Sources

  • CNACVSS 3.16.5read 2026-10-23
  • NVDCVSS 3.16.5read 2026-10-23
  • NVDCVSS 2.05.5read 2026-10-23
  • CNAweakness (CWE)CWE-372read 2026-10-23
  • FIRST EPSSEPSS score5.4 %2026-10-23
  • PoC-in-GitHubproof of concept1read 2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
Published
2021-09-06
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-25735?

A security issue was discovered in kube-apiserver that could allow node updates to bypass a Validating Admission Webhook. Clusters are only affected by this vulnerability if they run a Validating Admission Webhook for Nodes that denies admission based at least partially on the old state of the Node object. Validating Admission Webhook does not observe some previous fields.

Is CVE-2021-25735 actively exploited?

Active exploitation of CVE-2021-25735 has not been confirmed. Its EPSS score was 5.4% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-25735?

CVE-2021-25735 has a CVSS v3 base score of 6.5 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H.

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