A security issue was discovered in kube-apiserver that could allow node updates to bypass a Validating Admission Webhook. You are only affected by this vulnerability if you run a Validating Admission Webhook for Nodes that denies admission based at least partially on the old state of the Node object.

This issue has been rated Medium (CVSS:3.0/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H), and assigned CVE-2021-25735.

Note: This only impacts validating admission plugins that rely on old values in certain fields, and does not impact calls from kubelets that go through the built-in NodeRestriction admission plugin.

Affected Versions

• kube-apiserver v1.20.0 - v1.20.5
• kube-apiserver v1.19.0 - v1.19.9
• kube-apiserver <= v1.18.17

Fixed Versions

This issue is fixed in the following versions:

• kube-apiserver v1.21.0 - Fixed by refine validation #99946
• kube-apiserver v1.20.6 - Fixed by Automated cherry pick of #99946: tweak validation to avoid mutation #100315
• kube-apiserver v1.19.10 - Fixed by Automated cherry pick of #99946: tweak validation to avoid mutation #100316
• kube-apiserver v1.18.18 - Fixed by Automated cherry pick of #99946: tweak validation to avoid mutation #100317

Detection

If you find evidence that this vulnerability has been exploited, please contact security@kubernetes.io

Acknowledgements

This vulnerability was reported by Rogerio Bastos & Ari Lima from RedHat