CVE-2023-26484

### Impact If a malicious user has taken over a Kubernetes node where virt-handler (the KubeVirt node-daemon) is running, the virt-handler service account can be used to modify all node specs. This can be misused to lure-in system-level-privileged components (which can for instance read all secrets on the cluster, or can exec into pods on other nodes). This way a compromised node can be used to elevate privileges beyond the node until potentially having full privileged access to the whole cluster. The simplest way to exploit this, once a user could compromise a specific node, is to set with the virt-handler service account all other nodes to unschedulable and simply wait until system-critical components with high privileges appear on its node. Since this requires a node to be compromised first, the severity of this finding is considered Medium. ### Patches Not yet available. ### Workarounds Gatekeeper users can add a webhook which will block the `virt-handler` service account to modify the spec of a node. An example policy, preventing virt-handler from changing the node spec may look like this: ```yaml apiVersion: templates.gatekeeper.sh/v1 kind: ConstraintTemplate metadata: name: virthandlerrestrictions spec: [...] targets: - libs: - | [...] is_virt_handler(username) { username == "system:serviceaccount:kubevirt:virt-handler" } mutates_node_in_unintended_way { # TODO # only allow kubevirt.io/ prefixed metadata node changes } rego: | [...] violation[{"msg": msg}] { is_virt_handler(username) mutates_node_in_unintended_way(input.review.object, input.review.oldObject) msg := sprintf("virt-handler tries to modify node <%v> in an unintended way.", [input.review.object.name]) } ``` and applying this template to node modifications. ### Credits Special thanks to the discoverers of this issue: Nanzi Yang (nzyang@stu.xidian.edu.cn) Xin Guo (guox@stu.xidian.edu.cn) Jietao Xiao (jietaoXiao@stu.xidian.edu.cn) Wenbo Shen (shenwenbo@zju.edu.cn) Jinku Li (jkli@xidian.edu.cn) ### References https://github.com/kubevirt/kubevirt/issues/9109