Code inject via nginx.ingress.kubernetes.io/permanent-redirect annotation

Report Submission Form ## Summary: The value of the `nginx.ingress.kubernetes.io/permanent-redirect` annotation will be not sanitized and passed into the nginx configuration. This leads into a code inject from any user that is allowed to create ingress objects. ## Kubernetes Version: v1.26.3 (minikube) ## Component Version: ``` ------------------------------------------------------------------------------- NGINX Ingress controller Release: v1.8.0 Build: 35f5082ee7f211555aaff431d7c4423c17f8ce9e Repository: https://github.com/kubernetes/ingress-nginx nginx version: nginx/1.21.6 ------------------------------------------------------------------------------- ``` ## Steps To Reproduce: 1. Install ingress-nginx, using latest version and default values. For demo purpose, I set `allow-snippet-annotations=false` ```bash helm upgrade -i ingress-nginx ingress-nginx/ingress-nginx -f values.yaml # values.yaml is attached ``` 1. apply service and ingress object from attachments ```bash k apply -f ingress.yaml #ingress.yaml is attached ``` 1. Optional: If ingress-nginx is not exposed, run `kubectl port-forward deploy/ingress-nginx-controller 8080:80` and continue step 4 in a separate shell. 1. Validate, if the code is injected. This demo uses the hostname `kubernetes.api`, use the `--resolve` parameter of curl to do an request for the hidden server instance. The code below expect that ingress-nginx is accessible trough 127.0.0.1:8080 ```bash curl -v --resolve "kubernetes.api:8080:127.0.0.1" http://kubernetes.api:8080/api/v1/namespaces/kube-system/secrets/ ``` ## Supporting Material/References: * values.yaml - Used in step 1 * ingress.yaml - Used in step 2 ## Impact All users with access to create or update ingress objects, are able to running commands on ingress-nginx-controller pod. Since the token of the ServiceAccount is mounted on filesystem, a user can call the Kubernetes API and fetch all secrets or config maps from the cluster. Additionally, the user can read or write files to the filesystem.