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OpenAdvisories
Medium · 6.5 Public exploit CVE-2021-25735 EUVD-2021-1071GHSA-g42g-737j-qx6jGO-2022-0907

Validating Admission Webhook does not observe some previous fields

Published Sep 6, 2021 · Updated Sep 16, 2024 · Assigned by kubernetes

Vendor: Kubernetes Product: Kubernetes Package: k3s Package: k8s.io/kubernetes Package: kubernetes Ecosystem: Alpine Ecosystem: Debian Ecosystem: Go

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.

Affected products

VendorProductAffectedFixed
Kubernetes Kubernetes unspecified – ≤ 1.18.17, unspecified – ≤ 1.19.9, unspecified – ≤ 1.20.5 —

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

Debian

Security tracker ↗
ReleasePackageFixed inAdvisory
Debian 14 kubernetes 1.20.5+really1.20.2-1 —
Debian 13 kubernetes 1.20.5+really1.20.2-1 —
Debian 12 kubernetes 1.20.5+really1.20.2-1 —

Red Hat

Security tracker ↗
ReleasePackageFixed inAdvisory
Red Hat OpenShift 4 afterburn +1 5.0.0-1.rhaos4.8.el8 RHSA-2021:2437
Red Hat OpenShift 4 atomic-openshift-service-idler 4.8.0-202106281541.p0.git.39cfc66.assembly.stream.el8 RHSA-2021:2437
Red Hat OpenShift 4 butane 0.12.1-1.rhaos4.8.el8 RHSA-2021:2437
Red Hat OpenShift 4 console-login-helper-messages +2 0.20.3-1.rhaos4.8.el8 RHSA-2021:2437
Red Hat OpenShift 4 coreos-installer +1 0.9.0-6.rhaos4.8.el8 RHSA-2021:2437
Red Hat OpenShift 4 cri-o 1.21.2-5.rhaos4.8.gitb27d974.el7 RHSA-2021:2437
Red Hat OpenShift 4 cri-tools 1.21.0-2.el7 RHSA-2021:2437
Red Hat OpenShift 4 haproxy 2.2.13-1.el7 RHSA-2021:2437
Red Hat OpenShift 4 ignition +1 2.9.0-6.rhaos4.8.el8 RHSA-2021:2437
Red Hat OpenShift 4 ironic-images +3 2021.1-20210614.1.el8 RHSA-2021:2437
Red Hat OpenShift 4 jenkins 2.289.1.1624020353-1.el8 RHSA-2021:2437
Red Hat OpenShift 4 jenkins-2-plugins 4.8.1624022417-1.el8 RHSA-2021:2437
Red Hat OpenShift 4 kata-containers 2.1.0-4.el8 RHSA-2021:2437
Red Hat OpenShift 4 openshift +1 4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el7 RHSA-2021:2437
Red Hat OpenShift 4 openshift-ansible +1 4.8.0-202106281541.p0.git.626f7a3.assembly.stream.el7 RHSA-2021:2437
Red Hat OpenShift 4 openshift-clients +1 4.8.0-202106281541.p0.git.1077b05.assembly.stream.el7 RHSA-2021:2437
Red Hat OpenShift 4 openshift-kuryr +4 4.8.0-202106281541.p0.git.8a4c2d8.assembly.stream.el8 RHSA-2021:2437
Red Hat OpenShift 4 openstack-ironic +4 1:17.0.4-0.20210713221218.a415e7e.el8 RHSA-2021:2437
Red Hat OpenShift 4 openstack-ironic-inspector +4 10.6.1-0.20210406091336.579f59c.el8 RHSA-2021:2437
Red Hat OpenShift 4 openvswitch2.15 +3 2.15.0-9.el8fdp RHSA-2021:2437
Red Hat OpenShift 4 ostree +3 2020.7-5.el8_4 RHSA-2021:2437
Red Hat OpenShift 4 ovn2.13 +3 20.12.0-25.el8fdp RHSA-2021:2437
Red Hat OpenShift 4 podman +3 3.0.1-6.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-debtcollector +1 2.2.0-0.20210324220630.649189d.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-eventlet +1 0.25.2-4.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-hardware +2 0.27.0-0.20210406121246.756fedb.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-ironic-lib +1 4.6.2-0.20210608101214.ca2e4ba.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-ironic-prometheus-exporter +1 2.2.1-0.20210325143713.70e39c8.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-jsonschema +1 3.2.0-5.el8ost RHSA-2021:2437
Red Hat OpenShift 4 python-keystoneauth1 +1 4.3.0-0.20210325001456.6a66271.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-kubernetes +2 12.0.1-1.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-openshift +1 1:0.12.1-1.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-openstacksdk +2 0.53.0-0.20210325011601.4629245.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-concurrency +3 4.4.0-0.20210325004915.7dcf9e9.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-config +1 2:8.5.0-0.20210325050501.cfa2564.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-context +1 3.2.0-0.20210325043103.0d02866.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-db +3 8.5.0-0.20210325041241.503db60.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-i18n +2 5.0.1-0.20210324221600.73187bd.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-log +3 4.4.0-0.20210409081224.9b29c90.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-policy +2 3.7.0-0.20210325051823.d853485.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-serialization +2 4.1.0-0.20210325012242.8445e61.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-service +2 2.5.0-0.20210325014731.d25e454.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-upgradecheck +1 1.3.0-0.20210325003851.9f95a6e.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-oslo-utils +3 4.8.0-0.20210325043201.3288539.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-pyrsistent +1 0.16.0-3.el8ost RHSA-2021:2437
Red Hat OpenShift 4 python-stevedore +1 3.3.0-0.20210325001012.7d7154f.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-sushy +2 3.7.1-0.20210428165244.bc49878.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-sushy-oem-idrac +2 2.0.1-0.20210326152858.83b7eb0.el8 RHSA-2021:2437
Red Hat OpenShift 4 python-tooz +1 2.8.0-0.20210324235001.54448e9.el8 RHSA-2021:2437
Red Hat OpenShift 4 python3-ironic-python-agent +1 7.0.2-0.20210611153100.bfa97cb.el8 RHSA-2021:2437
Red Hat OpenShift 4 redhat-release-coreos 48.84-4.el8 RHSA-2021:2437
Red Hat OpenShift 4 rteval-loads 1.4-12.el8 RHSA-2021:2437
Red Hat OpenShift 4 runc 1.0.0-98.rhaos4.8.gitcd80260.el7 RHSA-2021:2437
Red Hat OpenShift 4 stress-ng 0.12.06-1.el8 RHSA-2021:2437
Red Hat OpenShift 4 toolbox 0.0.8-3.rhaos4.8.el8 RHSA-2021:2437

openSUSE

Security tracker ↗
ReleasePackageFixed inAdvisory
openSUSE Tumbleweed govulncheck-vulndb 0.0.20250807T150727-1.1 openSUSE-SU-2025:15424-1

Alpine

Security tracker ↗
ReleasePackageFixed inAdvisory
Alpine v3.24 k3s 1.20.6.1-r0 —
Alpine v3.23 k3s 1.20.6.1-r0 —
Alpine v3.22 k3s 1.20.6.1-r0 —
Alpine v3.21 k3s 1.20.6.1-r0 —
Alpine v3.20 k3s 1.20.6.1-r0 —
Show 6 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Alpine v3.19 k3s 1.20.6.1-r0 —
Alpine v3.18 k3s 1.20.6.1-r0 —
Alpine v3.17 k3s 1.20.6.1-r0 —
Alpine v3.16 k3s 1.20.6.1-r0 —
Alpine v3.15 k3s 1.20.6.1-r0 —
Alpine v3.14 k3s 1.20.6.1-r0 —

Public exploits

Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.

Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.

GitHub 1 repository

  • darryk10/CVE-2021-25735 ★ 17 · Apr 22, 2021

    Exploit CVE-2021-25735: Kubernetes Validating Admission Webhook Bypass

Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.

Affected packages

EcosystemPackageAffectedFixedRecord
Go k8s.io/kubernetes >= 1.20.0, < 1.20.6 1.20.6 GHSA-g42g-737j-qx6j
Go k8s.io/kubernetes >= 1.19.0, < 1.19.10 1.19.10 GHSA-g42g-737j-qx6j
Go k8s.io/kubernetes < 1.18.18 1.18.18 GHSA-g42g-737j-qx6j
Go k8s.io/kubernetes < 1.18.18 · >= 1.19.0, < 1.19.10 · >= 1.20.0, < 1.20.6 1.18.18, 1.19.10, 1.20.6 GO-2022-0907

Advisories 3

References