Impact

Before setting the sysctls for a pod, the pods namespaces must be unshared (created). However, in cases where the pod is using a host network or IPC namespace, a bug in CRI-O caused the namespace creating tool pinns to configure the sysctls of the host. This allows a malicious user to set sysctls on the host, assuming they have access to hostNetwork and hostIPC.

Any CRI-O cluster after CRI-O 1.18 that drops the infra container
1.22 and 1.23 clusters drop infra container by default, and are thus vulnerable by default.

Patches

CRI-O versions 1.24.0, 1.23.1, 1.22.2, 1.21.5, 1.20.6, 1.19.5 all have the patches.

Workarounds

Users can set manage_ns_lifecycle to false, which causes the sysctls to be configured by the OCI runtime, which typically filter these cases. This option is available in 1.20 and 1.19. Newer versions don't have this option.
An admission webhook could also be created to deny pods that use host IPC or network namespaces and also attempt to configure sysctls related to that namespace.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the CRI-O repo
• To make a report, email your vulnerability to the private
  cncf-crio-security@lists.cncf.io list
  with the security details and the details expected for all CRI-O bug
  reports.