CVE-2021-25737: Incomplete List of Disallowed Inputs in Kubernetes
Summary
CVE-2021-25737: Incomplete List of Disallowed Inputs in Kubernetes. Affects k8s.io/kubernetes across 4 version ranges.
>= 1.16.0, < 1.18.19
>= 1.19.0, < 1.19.11
>= 1.20.0, < 1.20.7
>= 1.21.0, < 1.21.1
Fixed in 4 releases; the minimum fixed version depends on the release line you run. How to fix ↓
Also tracked for
- kubernetes · Debian:11
The same CVE-2021-25737 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It is widely used in cloud-native environments to streamline the deployment and management of applications across clusters of machines. The vulnerability identified as CVE-2021-25737 affects the Kubernetes package and poses a moderate security risk. This vulnerability allows a user to redirect pod traffic to private networks on a Node. While Kubernetes already prevents the creation of Endpoint IPs in the localhost or link-local range, the same validation was not performed on EndpointSlice IPs.
Vulnerability Detail
The vulnerability arises from the lack of validation on EndpointSlice IPs in Kubernetes. By exploiting this flaw, an attacker can redirect pod traffic to private networks on a Node. This can lead to unauthorized access to sensitive resources and potential data breaches. The vulnerability has a CVSS score of 4.8, indicating a moderate severity level. It affects versions 1.16.0 to 1.18.19, 1.19.0 to 1.19.11, 1.20.0 to 1.20.7, and 1.21.0 to 1.21.1 of the Kubernetes package.
How To Fix
Latest published version: v1.37.1 as of 23 Oct 2026
go get k8s.io/kubernetes@v1.37.1Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
>= 1.16.0, < 1.18.191.18.19go get k8s.io/kubernetes@v1.18.19 -
>= 1.19.0, < 1.19.111.19.11go get k8s.io/kubernetes@v1.19.11 -
>= 1.20.0, < 1.20.71.20.7go get k8s.io/kubernetes@v1.20.7 -
>= 1.21.0, < 1.21.11.21.1go get k8s.io/kubernetes@v1.21.1
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
There is no specific workaround provided for this vulnerability. It is advised to update the Kubernetes package to the fixed versions as mentioned in the 'how_to_fix' section.
Conclusion
The vulnerability CVE-2021-25737 in the Kubernetes package poses a moderate security risk by allowing redirection of pod traffic to private networks on a Node. It is crucial to update the Kubernetes package to the fixed versions to mitigate the risk of exploitation. For further support on vulnerability remediation, please contact DevNack.com.
See every vulnerability recorded for k8s.io/kubernetes →
FAQ
Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications.
This vulnerability allows a user to redirect pod traffic to private networks on a Node, potentially leading to unauthorized access and data breaches.
The vulnerability has a CVSS score of 4.8, indicating a moderate severity level.
Versions 1.16.0 to 1.18.19, 1.19.0 to 1.19.11, 1.20.0 to 1.20.7, and 1.21.0 to 1.21.1 of the Kubernetes package are affected.
To fix this vulnerability, update the Kubernetes package to the fixed versions mentioned in the 'how_to_fix' section.
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