Webhook redirect in kube-apiserver

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Summary

CVECVE-2020-8561
StatePUBLISHED
Assignerkubernetes
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-09-20 17:15:08 UTC
Updated2026-06-01 23:16:14 UTC
DescriptionA security issue was discovered in Kubernetes where actors that control the responses of MutatingWebhookConfiguration or ValidatingWebhookConfiguration requests are able to redirect kube-apiserver requests to private networks of the apiserver. If that user can view kube-apiserver logs when the log level is set to 10, they can view the redirected responses and headers in the logs.

Risk And Classification

Primary CVSS: v3.1 4.1 MEDIUM from [email protected]

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

EPSS: 0.001830000 probability, percentile 0.397580000 (date 2026-06-02)

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

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary4.1MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:N/A:N
3.1[email protected]Secondary4.1MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:N/A:N
3.1CNADECLARED4.1MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:N/A:N
2.0[email protected]Primary4AV:N/AC:L/Au:S/C:P/I:N/A:N

CVSS v3.1 Breakdown

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

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

CVSS v2.0 Breakdown

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

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Kubernetes Kubernetes 1.20.11 - All All
Application Kubernetes Kubernetes 1.21.5 - All All
Application Kubernetes Kubernetes 1.22.2 - All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Kubernetes Kubernetes affected * semver Not specified

References

ReferenceSourceLinkTags
[Security Advisory] CVE-2020-8561: Webhook redirect in kube-apiserver af854a3a-2127-422b-91ae-364da2661108 groups.google.com Mailing List, Mitigation
CVE-2020-8561: Webhook redirect in kube-apiserver · Issue #104720 · 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-2020-8561 Kubernetes Vulnerability in NetApp Products | NetApp Product Security af854a3a-2127-422b-91ae-364da2661108 security.netapp.com Third Party Advisory
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: QiQi Xu (en)

Legacy QID Mappings

  • 376091 Kubernetes Webhook Redirect in kube-apiserver Vulnerability
  • 900491 Common Base Linux Mariner (CBL-Mariner) Security Update for kubernetes (7059)
  • 980585 Go (go) Security Update for k8s.io/kubernetes (GHSA-74j8-88mm-7496)
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