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                             CERT-Renater

                 Note d'Information No. 2021/VULN553
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DATE                : 22/10/2021

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running ingress-nginx versions prior to
                                      1.0.1, 0.49.1.

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https://groups.google.com/g/kubernetes-announce/c/6EZsyjpgRXk
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[Security Advisory] CVE-2021-25742: Ingress-nginx custom snippets allows
retrieval of ingress-nginx serviceaccount token and secrets across all
namespaces


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:

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

    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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