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Fencer Vulns
low 3.1

CVE-2021-25740 json

Holes in EndpointSlice Validation Enable Host Network Hijack

published 2021-09-20 5 y ago modified 2026-09-10 1 mo ago also GHSA-vw47-mr44-3jf9 , EUVD-2021-2120

cvss
3.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.0%
EPSS 2.0% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

A 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.

Patch / fix

  • kubernetes Debian 14, Debian 13, Debian 12 1.20.5+really1.20.2-1

debian advisories DEBIAN-CVE-2021-25740

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-25740 updated cvss 3.1

kubernetes: Endpoint & EndpointSlice permissions allow cross-Namespace forwarding

  • Red Hat OpenShift Container Platform 3.11 atomic-openshift, atomic-openshift-pod, atomic-openshift-node, atomic-openshift-tests, atomic-openshift-master, atomic-openshift-clients, +7 more
    affected: no fix planned “Out of support scope”
  • Red Hat OpenShift Container Platform 4 openshift, openshift-clients, openshift-kubelet, openshift-hyperkube, openshift-kube-apiserver, openshift-kube-scheduler, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.95% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 2.0 3.5 AV:N/AC:M/Au:S/C:P/I:N/A:N
GitHub 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem package affected fixed in
go k8s.io/kubernetes
<=1.22.2
 no fix listed

Affected products

  • Kubernetes Kubernetes

Classification

Weakness
  • CWE-441 Unintended Proxy or Intermediary
  • CWE-610 Externally Controlled Reference to a Resource in Another Sphere
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.