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

[CJ Cullen <cjcullen () google com>]

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
<https://www.first.org/cvss/calculator/3.1#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
   <https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#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
<https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/>


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 security () kubernetes io
Additional Details

See ingress-nginx Issue #7837
<https://github.com/kubernetes/ingress-nginx/issues/7837> for more details.
Acknowledgements

This vulnerability was reported by Mitch Hulscher.

Thank You,

CJ Cullen on behalf of the Kubernetes Security Response Committee