Security readout for executives and security teams
Plain-English summary
This Kubernetes API server flaw can let highly privileged node updates bypass a specific kind of validating admission webhook. It matters when an organization relies on webhooks to block Node changes by comparing the new request to the previous Node state.
Executive priority
Prioritize review in Kubernetes environments where Node admission controls enforce security policy. The issue is not broadly exposed by default, but it can weaken controls that protect cluster integrity and availability.
Technical view
kube-apiserver may fail to present some previous Node fields to Validating Admission Webhooks. Affected clusters are those using Node webhooks that deny admission based partly on old Node object state. CVSS 6.5 reflects network reachability, low complexity, high required privileges, and high integrity and availability impact.
Likely exposure
Exposure appears limited to Kubernetes clusters with Validating Admission Webhooks covering Node updates and relying on prior Node state. Clusters without that design are not described as affected in the source bundle.
Exploitation context
The source bundle does not show KEV listing or active exploitation evidence. The CVSS vector requires high privileges, so this is most relevant to already privileged Kubernetes identities or compromised automation able to update Node objects.
Researcher notes
Evidence is specific but incomplete on exact fixed versions in the provided bundle. Focus analysis on admission webhook behavior for Node updates, old-object state dependencies, and vendor advisories rather than assuming all Kubernetes clusters are affected.
Mitigation direction
- Review Kubernetes security advisory and distribution guidance for fixed versions.
- Inventory ValidatingWebhookConfiguration rules that apply to Node resources.
- Identify Node admission logic that depends on previous object state.
- Upgrade kube-apiserver following vendor guidance if your version is affected.
- Do not rely solely on affected webhook checks until remediated.
Validation and detection
- Confirm Kubernetes and kube-apiserver versions against vendor advisories.
- Review whether Node update webhooks compare old and new object state.
- Check admission and audit logs for unexpected accepted Node updates.
- Test remediated clusters with safe policy validation, not offensive payloads.
- Document whether each cluster matches the affected configuration.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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CWE-372: Exact CWE lookup
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Open ATT&CK lookupContainer behavior lookup
The affected technology mentions containers, so container-specific ATT&CK technique review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-25735 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H1.25.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://groups.google.com/g/kubernetes-security-announce/c/FKAGqT4jx9YCVE reference · x_refsource_MISC
- https://github.com/kubernetes/kubernetes/issues/100096CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Incomplete Internal State Distinction
Incomplete Internal State Distinction represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.