CVE-2021-25737Network attack vector

Pod traffic redirection via unvalidated EndpointSlice addresses

Published Sep 6, 2021 · Updated Sep 16, 2024

Input validation in Kubernetes kube-apiserver allows remote authenticated users to redirect pod traffic to private node networks. The API server accepts EndpointSlice addresses in the 127.0.0.0/8 and 169.254.0.0/16 ranges even though equivalent Endpoint addresses are rejected. Exploitation requires permission to create or modify EndpointSlices and can route Service traffic to localhost or link-local services on a node.

CVSS severity2.7
Low
EPSS probability1.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Input validation in Kubernetes kube-apiserver allows remote authenticated users to redirect pod traffic to private node networks. The API server accepts EndpointSlice addresses in the 127.0.0.0/8 and 169.254.0.0/16 ranges even though equivalent Endpoint addresses are rejected. Exploitation requires permission to create or modify EndpointSlices and can route Service traffic to localhost or link-local services on a node.

The record

CVE
CVE-2021-25737
Published
Sep 6, 2021
Updated
Sep 16, 2024
Vendor
Kubernetes
Product
Kubernetes
Classifications
CWE-184, CWE-601
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=1.18.18
  2. Affected versionversion=unspecified <=1.19.10
  3. Affected versionversion=unspecified <=1.20.6
  4. Affected versionversion=unspecified <=1.21.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Kubernetes · Kubernetesversion=unspecified <=1.18.18; version=unspecified <=1.19.10; version=unspecified <=1.20.6; version=unspecified <=1.21.0

Published CVSS scores

4.8NISTCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
4.9NISTAV:N/AC:M/Au:S/C:P/I:P/A:N
2.7KubernetesCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-184Incomplete List of Disallowed Inputs
CWE-601URL Redirection to Untrusted Site ('Open Redirect')

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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