VM applications can be shared with other subscriptions and tenants. If an application is being shared it's probably because it's being used. So if the attacker manages to compromise the application and uploads a backdoored version it might be possible that it will be executed in another tenant or subscription.
Sensitive information in images
It might be possible to find sensitive information inside images taken from VMs in the past.
List images from galleries
# Get galleriesazsiglist-otable# List images inside galleryazsigimage-definitionlist \--resource-group<RESOURCE_GROUP> \--gallery-name<GALLERY_NAME> \-otable# Get images versionsazsigimage-versionlist \--resource-group<RESOURCE_GROUP> \--gallery-name<GALLERY_NAME> \--gallery-image-definition<IMAGE_DEFINITION> \-otable
List custom images
azimagelist-otable
Create VM from image ID and search for sensitive info inside of it
# Create VM from imageazvmcreate \--resource-group<RESOURCE_GROUP> \--name<VM_NAME> \--image/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCE_GROUP>/providers/Microsoft.Compute/galleries/<GALLERY_NAME>/images/<IMAGE_DEFINITION>/versions/<IMAGE_VERSION> \--admin-username<ADMIN_USERNAME> \--generate-ssh-keys
Sensitive information in restore points
It might be possible to find sensitive information inside restore points.