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GCP - Storage Post Exploitation

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Cloud Storage

For more information about CLoud Storage check this page:

{{#ref}} ../gcp-services/gcp-storage-enum.md {{#endref}}

Give Public Access

It's possible to give external users (logged in GCP or not) access to buckets content. However, by default bucket will have disabled the option to expose publicly a bucket:

# Disable public prevention
gcloud storage buckets update gs://BUCKET_NAME --no-public-access-prevention

# Make all objects in a bucket public
gcloud storage buckets add-iam-policy-binding gs://BUCKET_NAME --member=allUsers --role=roles/storage.objectViewer
## I don't think you can make specific objects public just with IAM

# Make a bucket or object public (via ACL)
gcloud storage buckets update gs://BUCKET_NAME --add-acl-grant=entity=AllUsers,role=READER
gcloud storage objects update gs://BUCKET_NAME/OBJECT_NAME --add-acl-grant=entity=AllUsers,role=READER

If you try to give ACLs to a bucket with disabled ACLs you will find this error: ERROR: HTTPError 400: Cannot use ACL API to update bucket policy when uniform bucket-level access is enabled. Read more at https://cloud.google.com/storage/docs/uniform-bucket-level-access

To access open buckets via browser, access the URL https://<bucket_name>.storage.googleapis.com/ or https://<bucket_name>.storage.googleapis.com/<object_name>

storage.objects.delete (storage.objects.get)

To delete an object:

gcloud storage rm gs://<BUCKET_NAME>/<OBJECT_NAME> --project=<PROJECT_ID>

storage.buckets.delete, storage.objects.delete & storage.objects.list

To delete a bucket:

gcloud storage rm -r gs://<BUCKET_NAME>

Deactivate HMAC Keys

The storage.hmacKeys.update permission allows disabling HMAC keys, and the storage.hmacKeys.delete permission allows an identity to delete HMAC keys associated with service accounts in Cloud Storage.

# Deactivate
gcloud storage hmac update <ACCESS_ID> --deactivate

# Delete
gcloud storage hmac delete <ACCESS_ID>

storage.buckets.setIpFilter & storage.buckets.update

The storage.buckets.setIpFilter permission, together with the storage.buckets.update permission, allows an identity to configure IP address filters on a Cloud Storage bucket, specifying which IP ranges or addresses are allowed to access the bucket’s resources.

To completely clear the IP filter, the following command can be used:

gcloud storage buckets update gs://<BUCKET_NAME> --project=<PROJECT_ID>

To change the filtered IPs, the following command can be used:

gcloud storage buckets update gs://<BUCKET_NAME> \
  --ip-filter-file=ip-filter.json \
  --project=<PROJECT_ID>

The JSON file represents the filter itself, something like:

{
  "mode": "Enabled",
  "publicNetworkSource": {
    "allowedIpCidrRanges": ["<IP>/<MASK>"]
  },
  "allowCrossOrgVpcs": false,
  "allowAllServiceAgentAccess": false
}

storage.buckets.restore

Restore a bucket using:

gcloud storage restore gs://<BUCKET_NAME>#<GENERATION> \
  --project=<PROJECT_ID>

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