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Network Services Pentesting
GCP - Compute Enumeration
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Compute instances

It would be interesting if you can get the zones the project is using and the list of all the running instances and details about each of them.
The details may include:
  • Network info: Internal and external IP addresses, network and subnetwork names and security group
  • Custom key/values in the metadata of the instance
  • Protection information like shieldedInstanceConfig and shieldedInstanceIntegrityPolicy
  • Screenshot and the OS running
  • Try to ssh into it and try to modify the metadata
# Get list of zones
# It's interesting to know which zones are being used
gcloud compute regions list | grep -E "NAME|[^0]/"
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# List compute instances & get info
gcloud compute instances list
gcloud compute instances describe <instance name> --project <project name>
gcloud compute instances get-screenshot <instance name> --project <project name>
gcloud compute instances os-inventory list-instances #Get OS info of instances (OS Config agent is running on instances)
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# Try to SSH & modify metadata
gcloud compute ssh <instance>
gcloud compute instances add-metadata [INSTANCE] --metadata-from-file ssh-keys=meta.txt
For more information about how to SSH or modify the metadata of an instance to escalate privileges check this page:

Custom Metadata

Administrators can add custom metadata at the instance and project level. This is simply a way to pass arbitrary key/value pairs into an instance, and is commonly used for environment variables and startup/shutdown scripts. This can be obtained using the describe method from a command in the previous section, but it could also be retrieved from the inside of the instance accessing the metadata endpoint.
# view project metadata
curl "http://metadata.google.internal/computeMetadata/v1/project/attributes/?recursive=true&alt=text" \
-H "Metadata-Flavor: Google"
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# view instance metadata
curl "http://metadata.google.internal/computeMetadata/v1/instance/attributes/?recursive=true&alt=text" \
-H "Metadata-Flavor: Google"

Serial Console Logs

Compute instances may be writing output from the OS and BIOS to serial ports. Serial console logs may expose sensitive information from the system logs which low privileged user may not usually see, but with the appropriate IAM permissions you may be able to read them.
You can use the following gcloud command to query the serial port logs:
gcloud compute instances get-serial-port-output instance-name \
--port port \
--start start \
--zone zone
$ gcloud compute images export --image test-image \
--export-format qcow2 --destination-uri [BUCKET]
You can then export the virtual disks from any image in multiple formats. The following command would export the image test-image in qcow2 format, allowing you to download the file and build a VM locally for further investigation:
$ gcloud compute images list --no-standard-images

Local Privilege Escalation and Pivoting

If you compromises a compute instance you should also check the actions mentioned in this page:

Images

Custom Images

Custom compute images may contain sensitive details or other vulnerable configurations that you can exploit. You can query the list of non-standard images in a project with the following command:
gcloud compute images list --no-standard-images
You can then export the virtual disks from any image in multiple formats. The following command would export the image test-image in qcow2 format, allowing you to download the file and build a VM locally for further investigation:
gcloud compute images export --image test-image \
--export-format qcow2 --destination-uri [BUCKET]
# Execute container inside a docker
docker run --rm -ti gcr.io/<project-name>/secret:v1 sh
More generic enumeration:
gcloud compute images list
gcloud compute images list --project windows-cloud --no-standard-images #non-Shielded VM Windows Server images
gcloud compute images list --project gce-uefi-images --no-standard-images #available Shielded VM images, including Windows images

Custom Instance Templates

An instance template defines instance properties to help deploy consistent configurations. These may contain the same types of sensitive data as a running instance's custom metadata. You can use the following commands to investigate:
# List the available templates
$ gcloud compute instance-templates list
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# Get the details of a specific template
$ gcloud compute instance-templates describe [TEMPLATE NAME]

More Enumeration

Description
Command
Stop an instance
gcloud compute instances stop instance-2
Start an instance
gcloud compute instances start instance-2
Create an instance
gcloud compute instances create vm1 --image image-1 --tags test --zone "<zone>" --machine-type f1-micro
Download files
gcloud compute copy-files example-instance:~/REMOTE-DIR ~/LOCAL-DIR --zone us-central1-a
Upload files
gcloud compute copy-files ~/LOCAL-FILE-1 example-instance:~/REMOTE-DIR --zone us-central1-a
List all disks
gcloud compute disks list
List all disk types
gcloud compute disk-types list
List all snapshots
gcloud compute snapshots list
Create snapshot
gcloud compute disks snapshot --snapshotname --zone $zone
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