Holes in EndpointSlice Validation Enable Host Network Hijack

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Summary

CVECVE-2021-25740
StatePUBLISHED
Assignerkubernetes
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-09-20 17:15:08 UTC
Updated2026-06-01 23:16:15 UTC
DescriptionA security issue was discovered with Kubernetes that could enable users to send network traffic to locations they would otherwise not have access to via a confused deputy attack.

Risk And Classification

Primary CVSS: v3.1 3.1 LOW from [email protected]

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS: 0.005190000 probability, percentile 0.671820000 (date 2026-06-07)

Problem Types: CWE-441 | CWE-610 | CWE-441 CWE-441 Unintended Proxy or Intermediary

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary3.1LOWCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
3.1[email protected]Secondary3.1LOWCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
3.1CNADECLARED3.1LOWCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
2.0[email protected]Primary3.5AV:N/AC:M/Au:S/C:P/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS v2.0 Breakdown

Access Vector
Network
Access Complexity
Medium
Authentication
Single
Confidentiality
Partial
Integrity
None
Availability
None

AV:N/AC:M/Au:S/C:P/I:N/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Kubernetes Kubernetes - All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Kubernetes Kubernetes affected * semver Not specified

References

ReferenceSourceLinkTags
[Security Advisory] CVE-2021-25740: Endpoint & EndpointSlice permissions allow cross-Namespace forwarding af854a3a-2127-422b-91ae-364da2661108 groups.google.com Mailing List, Mitigation, Third Party Advisory
CVE-2021-25740 Kubernetes Vulnerability in NetApp Products | NetApp Product Security af854a3a-2127-422b-91ae-364da2661108 security.netapp.com Third Party Advisory
CVE-2021-25740: Endpoint & EndpointSlice permissions allow cross-Namespace forwarding · Issue #103675 · kubernetes/kubernetes · GitHub af854a3a-2127-422b-91ae-364da2661108 github.com Mitigation, Third Party Advisory
kubernetes.io/blog/2026/05/26/reconciling-unfixed-kubernetes-cves [email protected] kubernetes.io
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Rob Scott (en)

Legacy QID Mappings

  • 180887 Debian Security Update for kubernetes (CVE-2021-25740)
  • 980584 Go (go) Security Update for k8s.io/kubernetes (GHSA-vw47-mr44-3jf9)

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