Security readout for executives and security teams
Plain-English summary
Kubernetes disclosed a low-severity EndpointSlice validation issue that could let an authorized user redirect cluster network traffic to destinations they should not otherwise reach. This is mainly a concern in multi-tenant clusters or environments where less-trusted users can manage EndpointSlices.
Executive priority
Treat as a governance and tenancy-hardening issue, not an emergency. Prioritize review in shared Kubernetes environments or where application teams have broad cluster write permissions.
Technical view
CVE-2021-25740 is a confused-deputy issue in Kubernetes EndpointSlice validation. The provided CVSS vector requires network access, low privileges, no user interaction, high attack complexity, and has limited confidentiality impact. The source bundle does not provide specific affected release ranges or a confirmed fixed version.
Likely exposure
Exposure is most likely where Kubernetes users or workloads have permission to create or update EndpointSlices, especially in shared clusters with weaker RBAC separation.
Exploitation context
The source bundle does not show KEV listing or active exploitation evidence. Exploitation requires privileges and high complexity, limiting broad opportunistic risk.
Researcher notes
Evidence is limited to the supplied CVE metadata and references. The bundle identifies Kubernetes, CWE-441, CVSS 3.1 score 3.1, and no KEV status. It does not provide exploit details, fixed releases, or observed attacks.
Mitigation direction
- Check Kubernetes vendor guidance for affected versions and fixes.
- Audit RBAC permissions for EndpointSlice create and update access.
- Limit EndpointSlice management to trusted controllers and administrators.
- Review managed Kubernetes provider advisories for inherited exposure.
Validation and detection
- Inventory Kubernetes clusters and versions in use.
- Identify subjects with EndpointSlice write permissions.
- Review audit logs for unusual EndpointSlice changes.
- Confirm provider or vendor status for CVE-2021-25740.
Public sources used
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
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-441: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
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-2021-25740 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Low
- CVSS
- 3.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
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:H/PR:L/UI:N/S:U/C:L/I:N/A:N1.61.4kubernetesVulnerability scoring details
Base CVSS 3.1 score
3.1LowVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://kubernetes.io/blog/2026/05/26/reconciling-unfixed-kubernetes-cves/CVE reference, kubernetes · x_refsource_MISC
- https://groups.google.com/g/kubernetes-security-announce/c/WYE9ptrhSLECVE reference, kubernetes · x_refsource_MISC
- https://github.com/kubernetes/kubernetes/issues/103675CVE reference, kubernetes · x_refsource_MISC
- https://security.netapp.com/advisory/ntap-20211014-0001/CVE reference, kubernetes · x_refsource_CONFIRM
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.
Unintended Proxy or Intermediary ('Confused Deputy')
Unintended Proxy or Intermediary ('Confused Deputy') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.