[Security Advisory] CVE-2021-25742: Ingress-nginx custom snippets allows retrieval of ingress-nginx serviceaccount token and secrets across all namespaces

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CJ Cullen

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Oct 21, 2021, 12:24:34 PM10/21/21
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Hello Kubernetes Community,

A security issue was discovered in ingress-nginx where a user that can create or update ingress objects can use the custom snippets feature to obtain all secrets in the cluster.

This issue has been rated High (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L), and assigned CVE-2021-25742.

Affected Components and Configurations

This bug affects ingress-nginx.


Multitenant environments where non-admin users have permissions to create Ingress objects are most affected by this issue.

Affected Versions with no mitigation

  • v1.0.0

  • <= v0.49.0

Versions allowing mitigation

This issue cannot be fixed solely by upgrading ingress-nginx. It can be mitigated in the following versions:

  • v1.0.1

  • v0.49.1

Mitigation

To mitigate this vulnerability:

  1. Upgrade to a version that allows mitigation, (>= v0.49.1 or >= v1.0.1)

  2. Set allow-snippet-annotations to false in your ingress-nginx ConfigMap based on how you deploy ingress-nginx:


Static Deploy Files 


Edit the ConfigMap for ingress-nginx after deployment 


kubectl edit configmap -n ingress-nginx ingress-nginx-controller


Add directive:


data:

  allow-snippet-annotations: “false”

 

More information on the ConfigMap here 


Deploying Via Helm


Set controller.allowSnippetAnnotations to false in the Values.yaml or add the directive to the helm deploy:


helm install [RELEASE_NAME] --set controller.allowSnippetAnnotations=false ingress-nginx/ingress-nginx


https://github.com/kubernetes/ingress-nginx/blob/controller-v1.0.1/charts/ingress-nginx/values.yaml#L76


Detection

If you find evidence that this vulnerability has been exploited, please contact secu...@kubernetes.io

Additional Details

See ingress-nginx Issue #7837 for more details.

Acknowledgements

This vulnerability was reported by Mitch Hulscher.


Thank You,

CJ Cullen on behalf of the Kubernetes Security Response Committee

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