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Fencer Vulns
medium 6.5

CVE-2021-25735 json

Validating Admission Webhook does not observe some previous fields

published 2021-05-28 5 y ago modified 2026-09-10 1 mo ago also GHSA-g42g-737j-qx6j , GO-2022-0907 , EUVD-2021-1071

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
5.4%
EPSS 5.4% chance of exploitation in 30 days, percentile 92%
public exploits
0
none known

Summary

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.

Patch / fix

  • go k8s.io/kubernetes 1.18.18, 1.19.10, 1.20.6
  • kubernetes kubernetes 1.18.18, 1.19.10, 1.20.6
  • kubernetes Debian 14, Debian 13, Debian 12 1.20.5+really1.20.2-1

debian advisories DEBIAN-CVE-2021-25735

  • runc openshift 4.8 1.0.0-98.rhaos4.8.gitcd80260.el7
  • runc openshift 4.8 1.0.0-98.rhaos4.8.gitcd80260.el8
  • cri-o openshift 4.8 1.21.2-5.rhaos4.8.gitb27d974.el7
  • cri-o openshift 4.8 1.21.2-5.rhaos4.8.gitb27d974.el8
  • butane openshift 4.8 0.12.1-1.rhaos4.8.el8
  • ostree openshift 4.8 2020.7-5.el8_4
  • podman openshift 4.8 3.0.1-6.el8
  • haproxy openshift 4.8 2.2.13-1.el7

red hat advisories RHSA-2021:2437

  • govulncheck-vulndb openSUSE Tumbleweed 0.0.20250807T150727-1.1

opensuse advisories openSUSE-SU-2025:15424-1

  • k3s Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 1.20.6.1-r0

alpine advisories ALPINE-CVE-2021-25735

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kube-apiserver Arch Linux 1.21.0-1

arch linux advisories AVG-1825

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-25735 updated cvss 6.5

kubernetes: Validating Admission Webhook does not observe some previous fields

  • Red Hat OpenShift Container Platform 3.11 atomic-openshift, atomic-openshift-pod, atomic-openshift-node, atomic-openshift-tests, atomic-openshift-master, atomic-openshift-clients, +7 more
    affected: no fix planned “Will not fix”
  • Red Hat OpenShift Container Platform 4.8 openshift 4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el7, openshift 4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8, openshift-hyperkube 4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el7, openshift-hyperkube 4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8
    fixed: vendor fix RHSA-2021:2437
  • Red Hat OpenShift Container Platform 4.8 podman 3.0.1-6.el8, haproxy 2.2.13-1.el7, haproxy 2.2.13-1.el8, ostree 2020.7-5.el8_4, cri-tools 1.21.0-2.el7, cri-tools 1.21.0-2.el8, +130 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

5.38% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
NVD 2.0 5.5 AV:N/AC:L/Au:S/C:N/I:P/A:P
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H

Affected packages

ecosystem package affected fixed in
go k8s.io/kubernetes
>=1.20.0, <1.20.6
>=1.19.0, <1.19.10
<1.18.18
1.20.6
1.19.10
1.18.18

Affected products

  • Kubernetes Kubernetes

Classification

Weakness
  • CWE-372 Incomplete Internal State Distinction
  • CWE-284 Improper Access Control
  • CWE-863 Incorrect Authorization
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.