Is CVE-2021-25736 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2021-25736 being exploited in the wild.

How severe is CVE-2021-25736?

Medium severity, with a CVSS score of 5.8, published 30 October 2023.

Which products and versions are affected?

k8s.io/kubernetes (Go) < 1.21.0, SEMVER:introduced=0,fixed=1.21.0; Kubernetes < 1.21.0.

Is there a fix for CVE-2021-25736?

Yes. k8s.io/kubernetes (Go): upgrade to 1.21.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2021-25736 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2021-25736?

Check whether you run k8s.io/kubernetes (Go) or Kubernetes at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2021-25736: Kubernetes kube-proxy traffic forwarding error on Windows

Q: Is there a fix for CVE-2021-25736?

Yes. k8s.io/kubernetes (Go): upgrade to 1.21.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2021-25736 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2021-25736?

Check whether you run k8s.io/kubernetes (Go) or Kubernetes at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2021-25736 · Severity: medium · CVSS 5.8 · Published 2023-10-30

A vulnerability in the Kubernetes networking component for Windows could allow network traffic to be misdirected to unintended local processes. This occurs when specific load balancer settings are missing, potentially allowing an attacker with high privileges to intercept data intended for legitimate services. This could lead to unauthorized access to sensitive information within the cluster environment.

Technologies: k8s.io/kubernetes (Go), Kubernetes. Vendors: Go, Kubernetes.

Quick answers

Is CVE-2021-25736 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2021-25736 being exploited in the wild.
How severe is CVE-2021-25736?: Medium severity, with a CVSS score of 5.8, published 30 October 2023.
Which products and versions are affected?: k8s.io/kubernetes (Go) < 1.21.0, SEMVER:introduced=0,fixed=1.21.0; Kubernetes < 1.21.0.
Is there a fix for CVE-2021-25736?: Yes. k8s.io/kubernetes (Go): upgrade to 1.21.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2021-25736 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2021-25736?: Check whether you run k8s.io/kubernetes (Go) or Kubernetes at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

k8s.io/kubernetes (Go): upgrade to 1.21.0 or later
```
go get k8s.io/kubernetes@v1.21.0
```

Technical details

A traffic misdirection vulnerability exists in kube-proxy on Windows nodes. The issue occurs when a LoadBalancer Service is created but the LoadBalancer controller fails to populate the `status.loadBalancer.ingress[].ip` field. In this scenario, kube-proxy may unintentionally forward traffic to local processes listening on the same port defined in `spec.ports[*].port`. Exploitation requires high privileges and specific network configurations (high complexity), but can result in a scope change allowing an attacker to intercept traffic. The issue is resolved in Kubernetes version 1.21.0.

Affected products

Kubernetes kubernetes < 1.21.0

Identifiers

CVE-2021-25736
GHSA-35c7-w35f-xwgh
GO-2023-2159

Timeline

2023-10-30: advisory
2023-10-30: disclosed
2021-04-08: patched: Based on Kubernetes 1.21.0 release date and commit history

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.