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CVE-2017-14491

A vulnerability in dnsmasq, used by kube-dns, requires an upgrade to the kube-dns component. This component is the default DNS component installed in Kubernetes. The vulnerability may be externally exploitable. Links below exist with the full detail of the CVE. This exploit is not a Kubernetes specific vulnerability but exists in dnsmasq.

Current kops Status

kops release 1.7.1 addresses this CVE. This version of kops will upgrade and create clusters. kops 1.8.0.alpha.1 release does not contain the required changes, but when released 1.8.0.apha.2 will contain the required patches.

Upgrading Cluster

The kube-dns deployment will be automatically upgraded when kops update cluster is executed. Replace my-cluster.example.com with the name of your cluster. If you are upgrading a Kubernetes 1.4.x or 1.5.x cluster you may need to follow the instruction below to create a required configmap for kube-dns.

Upgrade command:

kops update cluster --yes --name my-cluster.example.com

Validate the change was applied to the deployment:

kubectl get deployment -n kube-system kube-dns \
-o jsonpath='{.spec.template.spec.containers[?(@.name == "dnsmasq")].image}'

The upgrade will occur once the channels utility picks up the change within a few minutes.

Tested Kubernetes Versions

Kubernetes versions 1.5.8, 1.6.11, 1.7.7, and 1.8.0 have been fully tested with the new version of kube-dns deployment. Other versions should function, but upgrading to tested version is recommended. We have had 1.4.x users upgrade successfully, but we cannot validate full production stability. Local testing in a non-production environment is always recommended. We are not able to quantify the risk of using a non-tested version.

Fixed kops releases

We are planning to release in 1.8.x kops releases. 1.7.1 release is released with the needed changes. If you are using the 1.8.x alpha releases, we recommend applying the hotfixes.

Fixed kops Version Matrix

kops Version Fixed Released Will Fix URL
1.7.1 Y Y Not Applicable here
master Y N Not Applicable here
1.8.0 N N Y Not Applicable
1.8.0.alpha.1 N Y N Not Applicable
1.7.0 N Y N Not Applicable

kops PR fixes

  • Fixed by @mikesplain in #3511
  • Fixed by @mikesplain in #3538

kops Tracking Issue

  • Filed by @chrislovecnm #3512

Hotfix Instructions

The minimal fix is just to update the container for the pods using dnsmasq. You are able to apply this fix without downtime. Hotfix instruction differ between Kubernetes releases. The newer version of kube-dns includes the k8s-dns-dnsmasq-nanny-amd64 container.

Kubernetes Versions 1.6.x and higher

Installation of Hot Fix

Apply the update to the container:

kubectl set image deployment/kube-dns -n kube-system \
 dnsmasq=k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.5

Validate the change was applied to the deployment:

kubectl get deployment -n kube-system kube-dns \
 -o jsonpath='{.spec.template.spec.containers[?(@.name == "dnsmasq")].image}'

Validation

To verify that pods were deployed:

kubectl get pods -n kube-system -o \
 custom-columns=NAME:.metadata.name,IMAGE:.spec.containers[*].image \
 -l k8s-app=kube-dns

You should see version 1.14.5 for the k8s-dns-dnsmasq-nanny-amd64 container:

NAME                        IMAGE
kube-dns-1100866048-3lqm0   k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.5,k8s.gcr.io/k8s-dns-kube-dns-amd64:1.14.5,k8s.gcr.io/k8s-dns-sidecar-amd64:1.14.5
kube-dns-1100866048-tjlv2   k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.5,k8s.gcr.io/k8s-dns-kube-dns-amd64:1.14.5,k8s.gcr.io/k8s-dns-sidecar-amd64:1.14.5

Kubernetes Versions 1.4.x - 1.5.x

Check to see if you have the new configmap for kube-dns. A configmap is required for the 1.14.5 containers, and kube-dns will NOT start without the configmap.

Installation of Dependencies

kubectl -n kube-system get configmap kube-dns

If the configmap does not exist create an empty configmap.

Installation of Hot Fix

kubectl create configmap -n kube-system kube-dns

Upgrade the kube-dns container to the new version.

kubectl set image deployment/kube-dns -n kube-system \
 dnsmasq=k8s.gcr.io/k8s-dns-dnsmasq-amd64:1.14.5

Validate the change was applied to the deployment:

kubectl get deployment -n kube-system kube-dns \
 -o jsonpath='{.spec.template.spec.containers[?(@.name == "dnsmasq")].image}'

To verify that pods were deployed:

kubectl get pods -n kube-system -o \
 custom-columns=NAME:.metadata.name,IMAGE:.spec.containers[*].image \
  -l k8s-app=kube-dns

You should see version 1.14.5 for the dnsmasq pod

NAME                        IMAGE
kube-dns-4146767324-djthf   k8s.gcr.io/kubedns-amd64:1.9,k8s.gcr.io/k8s-dns-dnsmasq-amd64:1.14.5,k8s.gcr.io/dnsmasq-metrics-amd64:1.0,k8s.gcr.io/exechealthz-amd64:1.2
kube-dns-4146767324-kloxi   k8s.gcr.io/kubedns-amd64:1.9,k8s.gcr.io/k8s-dns-dnsmasq-amd64:1.14.5,k8s.gcr.io/dnsmasq-metrics-amd64:1.0,k8s.gcr.io/exechealthz-amd64:1.2

More Information

Thanks

Thanks to all that helped @mikesplain, @chrislovecnm, @snoby, @justinsb, @3h4x, @aaronlevy