Apache CloudStack: Uploaded and registered templates and volumes can be used to abuse KVM-based infrastructure

Summary

Account users in Apache CloudStack by default are allowed to upload and register templates for deploying instances and volumes for attaching them as data disks to their existing instances. Due to missing validation checks for KVM-compatible templates or volumes in CloudStack 4.0.0 through 4.18.2.3 and 4.19.0.0 through 4.19.1.1, an attacker that can upload or register templates and volumes, can use them to deploy malicious instances or attach uploaded volumes to their existing instances on KVM-based environments and exploit this to gain access to the host filesystems that could result in the compromise of resource integrity and confidentiality, data loss, denial of service, and availability of KVM-based infrastructure managed by CloudStack.

Users are recommended to upgrade to Apache CloudStack 4.18.2.4 or 4.19.1.2, or later, which addresses this issue.

Additionally, all user-uploaded or registered KVM-compatible templates and volumes can be scanned and checked that they are flat files that should not be using any additional or unnecessary features. For example, operators can run this on their secondary storage(s) and inspect output. An empty output for the disk being validated means it has no references to the host filesystems; on the other hand, if the output for the disk being validated is not empty, it might indicate a compromised disk.

for file in $(find /path/to/storage/ -type f -regex [a-f0-9\-]*.*); do echo "Retrieving file [$file] info. If the output is not empty, that might indicate a compromised disk; check it carefully."; qemu-img info -U $file | grep file: ; printf "\n\n"; done The command can also be run for the file-based primary storages; however, bear in mind that (i) volumes created from templates will have references for the templates at first and (ii) volumes can be consolidated while migrating, losing their references to the templates. Therefore, the command execution for the primary storages can show both false positives and false negatives.

For checking the whole template/volume features of each disk, operators can run the following command:

for file in $(find /path/to/storage/ -type f -regex [a-f0-9\-]*.*); do echo "Retrieving file [$file] info."; qemu-img info -U $file; printf "\n\n"; done