CVE-2020-14386

A flaw was found in the Linux kernel. Memory corruption can be exploited to gain root privileges from unprivileged processes. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Only local users with CAP_NET_RAW capability enabled can trigger this issue.

For OpenShift Container Platform 4, pods in the default restricted SCC are granted CAP_NET_RAW by default. An attacker can exploit this if they can run arbitrary container images on the target cluster.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

If the CAP_NET_RAW capability disabled by default (which is true for Red Hat Enterprise Linux), then only a privileged user can trigger this bug. The mitigation is to disable CAP_NET_RAW capability for regular users and for executables.

On Red Hat Enterprise Linux 8 CAP_NET_RAW capability can be also gained by exploiting unprivileged user namespaces. The mitigation is to disable unprivileged user namespaces by setting user.max_user_namespaces to 0:

echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf

sysctl -p /etc/sysctl.d/userns.conf

OpenShift Container Platform 4.5 and 4.4 this can be mitigated by removing CAP_NET_RAW from the default cri-o capabilities provided to pods (NOTE: This may prevent ping from working in unprivileged pods. This fix has not been validated for OpenShift 4.3 or below):

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 50-reset-crio-capabilities
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;charset=utf-8;base64,W2NyaW8ucnVudGltZV0KZGVmYXVsdF9jYXBhYmlsaXRpZXMgPSBbCiAgICAiQ0hPV04iLAogICAgIkRBQ19PVkVSUklERSIsCiAgICAiRlNFVElEIiwKICAgICJGT1dORVIiLAogICAgIlNFVEdJRCIsCiAgICAiU0VUVUlEIiwKICAgICJTRVRQQ0FQIiwKICAgICJORVRfQklORF9TRVJWSUNFIiwKICAgICJTWVNfQ0hST09UIiwKICAgICJLSUxMIiwKXQo=
        filesystem: root
        mode: 0644
        path: /etc/crio/crio.conf.d/reset-crio-capabilities.conf

Create this MachineConfig object via e.g. oc apply. More information about MachineConfig can be found here: https://github.com/openshift/machine-config-operator https://docs.openshift.com/container-platform/4.5/architecture/architecture-rhcos.html

In order to monitor the rollout of this change, use oc describe machineconfigpool/worker.

Check for any pods which start to crash after this is applied; they may need to be adjusted request CAP_NET_RAW explicitly. More information: https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-capabilities-for-a-container https://docs.openshift.com/container-platform/4.5/authentication/managing-security-context-constraints.html