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KubernetesApplication

CVE-2021-25736

MEDIUM · 6.3 CVSS v3.1 Published 2023-10-30
Fix available
A fix is available. Upgrade to 1.18.18 / 1.19.10 or later.
See remediation →
69/100
Remediation priority · Elevated
Remotely reachable Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Kube-proxy on Windows can unintentionally forward traffic to local processes listening on the same port (“spec.ports[*].port”) as a LoadBalancer Service when the LoadBalancer controller does not set the “status.loadBalancer.ingress[].ip” field. Clusters where the LoadBalancer controller sets the “status.loadBalancer.ingress[].ip” field are unaffected.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
KubernetesApplication
Affected:>= 1.18.0, < 1.18.18>= 1.19.0, < 1.19.10>= 1.20.0, < 1.20.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.18.18 / 1.19.10 / 1.20.6 or later
Fixed in 1.18.181.19.101.20.6
Vendor patch github.com →
Recommended fix High confidence

Kubernetes v1.18.18, v1.19.10, or v1.20.6 (or subsequent releases in each minor version line)

  1. Identify the current Kubernetes version in use: kubectl get nodes -o wide or check kubelet version
  2. Determine which affected version range your cluster falls into (1.18.x, 1.19.x, or 1.20.x)
  3. For clusters running 1.18.x: upgrade to Kubernetes v1.18.18 or later
  4. For clusters running 1.19.x: upgrade to Kubernetes v1.19.10 or later
  5. For clusters running 1.20.x: upgrade to Kubernetes v1.20.6 or later
  6. After upgrade, verify kube-proxy is running the corrected version on Windows nodes
  7. Test LoadBalancer services to confirm traffic is correctly routed
Caveat Patch releases typically have minimal breaking changes; however, always review release notes before upgrading and test in a staging environment

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-25736 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data