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Full vulnerability report · 2021
CVE-2021-25737High confidence

Holes in EndpointSlice Validation Enable Host Network Hijack

Kubernetes · Kubernetes

2.7LowCVSS 3.1
Recommended action
Scheduled

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityLowOperational priority:Low, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 1.33% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Kubernetes Kubernetes and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: No default targetRemediation target: Normal maintenance

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcekubernetesVendor fix publishedDebian records a fixed source-package version for this release.1.20.5+really1.20.2-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcekubernetesVendor fix publishedDebian records a fixed source-package version for this release.1.20.5+really1.20.2-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcekubernetesVendor fix publishedDebian records a fixed source-package version for this release.1.20.5+really1.20.2-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcekubernetesVendor fix publishedDebian records a fixed source-package version for this release.1.20.5+really1.20.2-1Debian Security Tracker ↗Source updated 6 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2021-25737 · CSAF 2.0 · revision 3 · status not statedRed Hat Product Securitykubernetes: Holes in EndpointSlice Validation Enable Host Network Hijack
6 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • openshift-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el7.src as a component of Red Hat OpenShift Container Platform 4.8
  • openshift-hyperkube-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el7.x86_64 as a component of Red Hat OpenShift Container Platform 4.8
  • openshift-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8.src as a component of Red Hat OpenShift Container Platform 4.8
  • openshift-hyperkube-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8.ppc64le as a component of Red Hat OpenShift Container Platform 4.8
  • openshift-hyperkube-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8.s390x as a component of Red Hat OpenShift Container Platform 4.8
  • openshift-hyperkube-0:4.8.0-202107161820.p0.git.051ac4f.assembly.stream.el8.x86_64 as a component of Red Hat OpenShift Container Platform 4.8
Summary
A security issue was discovered in Kubernetes where an authorized user may be able to redirect traffic to private networks on a Node. An untrusted user could exploit this by creating or modifying EndpointSlices to point to localhost or link-local addresses.
Remediation
For OpenShift Container Platform 4.8 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.openshift.com/container-platform/4.8/release_notes/ocp-4-8-release-notes.html Details on how to access this content are available at https://docs.openshift.com/container-platform/4.8/updating/updating-cluster-cli.html
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-2095

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

A security issue was discovered in Kubernetes where a user may be able to redirect pod traffic to private networks on a Node. Kubernetes already prevents creation of Endpoint IPs in the localhost or link-local range, but the same validation was not performed on EndpointSlice IPs.

What

A security issue was discovered in Kubernetes where a user may be able to redirect pod traffic to private networks on a Node. Kubernetes already prevents creation of Endpoint IPs in the localhost or link-local range, but the same validation was not performed on EndpointSlice IPs.

Why

The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.

How

An attacker operating through a network path may attempt exploitation with elevated privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

A security issue was discovered in Kubernetes where a user may be able to redirect pod traffic to private networks on a Node. Kubernetes already prevents creation of Endpoint IPs in the localhost or link-local range, but the same validation was not performed on EndpointSlice IPs.

Why

The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.

How

An attacker operating through a network path may attempt exploitation with elevated privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Incomplete List of Disallowed Inputs → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
High: elevated access is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-184 ↗

CWE-184: Incomplete List of Disallowed Inputs. The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRHighPrivileges required: The attacker needs elevated or administrative privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CLowConfidentiality impact: A successful attack can cause a limited loss.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkCWE-184
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2022-0510IBM DB2: Mehrere Schwachstellen

Ein entfernter, anonymer, authentisierter oder lokaler Angreifer kann mehrere Schwachstellen in IBM DB2 ausnutzen, um Dateien zu manipulieren, Sicherheitsmaßnahmen zu umgehen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Zustand auszulösen, willkürlichen Code mit erhöhten Rechten auszuführen, Informationen falsch darzustellen und beliebigen Code auszuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210908Security Bulletin 08 Sep 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 08 Sep 2021, published on 8 September 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2022-AVI-591Multiples vulnérabilités dans les produits IBM

cord?id=CVE-2020-8565 Référence CVE CVE-2020-9283 https://www.cve.org/CVERecord?id=CVE-2020-9283 Référence CVE CVE-2021-20206 https://www.cve.org/CVERecord?id=CVE-2021-20206 Référence CVE CVE-2021-20269 https://www.cve.org/CVERecord?id=CVE-2021-20269 Référence CVE CVE-2021-20321 https://www.cve.org/CVERecord?id=CVE-2021-20321 Référence CVE CVE-2021-20322 https://www.cve.org/CVERecord?id=CVE-2021-20322 Référence CVE CVE-2021-21781 https://www.cve.org/CVERecord?id=CVE-2021-21781 Référence CVE CVE-2021-25735 https://www.cve.org/CVERecord?id=CVE-2021-25735 Référence CVE CVE-2021-25736 https://www.cve.org/CVERecord?id=CVE-2021-25736 Référence CVE CVE-2021-25737 https://www.cve.org/CVERecord?id=CVE-2021-25737 Référence CVE CVE-2021-25741 https://www.cve.org/CVERecord?id=CVE-2021-25741 Référence CVE CVE-2021-27918 https://www.cve.org/CVERecord?id=CVE-2021-27918 Référence CVE CVE-2021-28950 https://www.cve.org/CVERecord?id=CVE-2021-28950 Référence CVE CVE-2021-28971 https://www.cve.org/CVERecord?id=CVE-2021-28971 Référence CVE CVE-2021-29650 https://www.cve.org/CVERecord?id=CVE-2021-29650 Référence CVE CVE-2021-30465 https://www.cve.org/CVERecord?id=CVE-2021-30465 Référence CVE CVE-2021-3121 https://www.cve.org/CVERecord?id=CVE-2021-3121 Référence CVE CVE-2021-31525 https://www.cve.org/CVERecord?id=CV

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-011442Kubernetes におけるオープンリダイレクトの脆弱性

Kubernetes には、オープンリダイレクトの脆弱性が存在します。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Kubernetes: unspecified ≤ 1.18.18, unspecified ≤ 1.19.10, unspecified ≤ 1.20.6, unspecified ≤ 1.21.0
Fixed
Action
For OpenShift Container Platform 4.8 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.openshift.com/container-platform/4.8/release_notes/ocp-4-8-release-notes.html Details on how to access this content are available at https://docs.openshift.com/container-platform/4.8/updating/updating-cluster-cli.html
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 6 Sept 2021 · Last source change 16 Sept 2024, 21:04 UTC · CWE-184 · Incomplete List of Disallowed Inputs

CVE recordCVE.org · 5.1
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-2095
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    unspecified ≤ 1.18.18; unspecified ≤ 1.19.10; unspecified ≤ 1.20.6; unspecified ≤ 1.21.0 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    unspecified ≤ 1.18.18; unspecified ≤ 1.19.10; unspecified ≤ 1.20.6; unspecified ≤ 1.21.0 · Fixed: For OpenShift Container Platform 4.8 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.openshift.com/container-platform/4.8/release_notes/ocp-4-8-release-notes.html Details on how to access this content are available at https://docs.openshift.com/container-platform/4.8/updating/updating-cluster-cli.html
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-2095↗Red Hat Product Security security advisory↗Patch or update reference↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-25737 · cve.blacktree.nl