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hacktricks/cloud-security/gcp-security/gcp-interesting-permissions/gcp-privesc-to-other-principals.md
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{% hint style="info" %} GCP has hundreds of permissions. This is just a list containing the known ones that could allow you to escalate to other principals.
If you know about any other permissions not mentioned here, please send a PR to add it or let me know and I will add it. {% endhint %}

IAM

iam.roles.update (iam.roles.get)

If you have the mentioned permissions you will be able to update a role assigned to you and give you extra permissions to other resources like:

gcloud iam roldes update <rol name> --project <project> --add-permissions <permission>

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here. For more information check the original research.

iam.serviceAccounts.getAccessToken (iam.serviceAccounts.get)

This permission allows to request an access token that belongs to a Service Account, so it's possible to request an access token of a Service Account with more privileges than ours.

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here. For more information check the original research.

iam.serviceAccountKeys.create

This permission allows us to do something similar to the previous method, but instead of an access token, we are creating a user-managed key for a Service Account, which will allow us to access GCP as that Service Account.

gcloud iam service-accounts keys create --iam-account <name>

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here. For more information check the original research.

Note that iam.serviceAccountKeys.update won't work to modify the key of a SA because to do that the permissions iam.serviceAccountKeys.create is also needed.

iam.serviceAccounts.implicitDelegation

If you have the iam.serviceAccounts.implicitDelegation** permission on a Service Account** that has the iam.serviceAccounts.getAccessToken** permission on a third Service Account**, then you can use implicitDelegation to create a token for that third Service Account. Here is a diagram to help explain.

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here. For more information check the original research.

Note that according to the documentation, the delegation only works to generate a token using the generateAccessToken() method.

iam.serviceAccounts.signBlob

The iam.serviceAccounts.signBlob permission “allows signing of arbitrary payloads” in GCP. This means we can create an unsigined JWT of the SA and then send it as a blob to get the JWT signed by the SA we are targeting. For more information read this.

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here and here. For more information check the original research.

iam.serviceAccounts.signJwt

Similar to how the previous method worked by signing arbitrary payloads, this method works by signing well-formed JSON web tokens (JWTs). The difference with the previous method is that instead of making google sign a blob containing a JWT, we use the signJWT method that already expects a JWT. This makes it easier to use but you can only sign JWT instead of any bytes.

You can find a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to abuse this privilege here. For more information check the original research.

iam.serviceAccounts.setIamPolicy

This permission allows to add IAM policies to service accounts. You can abuse it to grant yourself the permissions you need to impersonate the service account. In the following example we are granting ourselves the “roles/iam.serviceAccountTokenCreator” role over the interesting SA:

gcloud iam service-accounts add-iam-policy-binding "${VICTIM_SA}@${PROJECT_ID}.iam.gserviceaccount.com" \
	--member="user:username@domain.com" \
	--role="roles/iam.serviceAccountTokenCreator"

You can find a script to automate the creation, exploit and cleaning of a vuln environment here.

iam.serviceAccounts.actAs

This means that as part of creating certain resources, you must “actAs” the Service Account for the call to complete successfully. For example, when starting a new Compute Engine instance with an attached Service Account, you need iam.serviceAccounts.actAs on that Service Account. This is because without that permission, users could escalate permissions with fewer permissions to start with.

There are multiple individual methods that use _iam.serviceAccounts.actAs_, so depending on your own permissions, you may only be able to exploit one (or more) of these methods below. These methods are slightly different in that they require multiple permissions to exploit, rather than a single permission like all of the previous methods.

iam.serviceAccounts.getOpenIdToken

This permission can be used to generate an OpenID JWT. These are used to assert identity and do not necessarily carry any implicit authorization against a resource.

According to this interesting post, it's necessary to indicate the audience (service where you want to use the token to authenticate to) and you will receive a JWT signed by google indicating the service account and the audience of the JWT.

You can generate an OpenIDToken (if you have the access) with:

# First activate the SA with iam.serviceAccounts.getOpenIdToken over the other SA
gcloud auth activate-service-account --key-file=/path/to/svc_account.json
# Then, generate token
gcloud auth print-identity-token "${ATTACK_SA}@${PROJECT_ID}.iam.gserviceaccount.com" --audiences=https://example.com

Then you can just use it to access the service with:

curl -v -H "Authorization: Bearer id_token" https://some-cloud-run-uc.a.run.app

Some services that support authentication via this kind of tokens are:

You can find an example on how to create and OpenID token behalf a service account here.

resourcemanager

resourcemanager.organizations.setIamPolicy

Like in the exploitation of iam.serviceAccounts.setIamPolicy, this permission allows you to modify your permissions against any resource at organization level. So, you can follow the same exploitation example.

resourcemanager.folders.setIamPolicy

Like in the exploitation of iam.serviceAccounts.setIamPolicy, this permission allows you to modify your permissions against any resource at folder level. So, you can follow the same exploitation example.

resourcemanager.projects.setIamPolicy

Like in the exploitation of iam.serviceAccounts.setIamPolicy, this permission allows you to modify your permissions against any resource at project level. So, you can follow the same exploitation example.

deploymentmanager

deploymentmanager.deployments.create

This single permission lets you launch new deployments of resources into GCP with arbitrary service accounts. You could for example launch a compute instance with a SA to escalate to it.

You could actually launch any resource listed in gcloud deployment-manager types list

In the original research following script is used to deploy a compute instance, however that script won't work. Check a script to automate the creation, exploit and cleaning of a vuln environment here.

deploymentmanager.deployments.update

This is like the previous abuse but instead of creating a new deployment, you modifies one already existing (so be careful)

Check a script to automate the creation, exploit and cleaning of a vuln environment here.

deploymentmanager.deployments.setIamPolicy

This is like the previous abuse but instead of directly creating a new deployment, you first give you that access and then abuses the permission as explained in the previos deploymentmanager.deployments.create section.

cloudbuild

cloudbuild.builds.create

With this permission you can submit a cloud build. The cloudbuild machine will have in it’s filesystem by default a token of the powerful cloudbuild Service Account: <PROJECT_NUMBER>@cloudbuild.gserviceaccount.com . However, you can indicate any service account inside the project in the cloudbuild configuration.
Therefore, you can just make the machine exfiltrate to your server the token or get a reverse shell inside of it and get yourself the token (the file containing the token might change).

You can find the original exploit script here on GitHub (but the location it's taking the token from didn't work for me). Therefore, check a script to automate the creation, exploit and cleaning of a vuln environment here and a python script to get a reverse shell inside of the cloudbuild machine and steal it here (in the code you can find how to specify other service accounts).

For a more in-depth explanation visit https://rhinosecuritylabs.com/gcp/iam-privilege-escalation-gcp-cloudbuild/

cloudbuild.builds.update

Potentially with this permission you will be able to update a cloud build and just steal the service account token like it was performed with the previous permission (but unfortunately at the time of this writing I couldn't find any way to call that API).

compute

compute.projects.setCommonInstanceMetadata

With that permission you can modify the metadata information of an instance and change the authorized keys of a user, or create a new user with sudo permissions. Therefore, you will be able to exec via SSH into any VM instance and steal the GCP Service Account the Instance is running with.
Limitations:

  • Note that GCP Service Accounts running in VM instances by default have a very limited scope
  • You will need to be able to contact the SSH server to login

For more information about how to exploit this permission check:

{% content-ref url="../gcp-local-privilege-escalation-ssh-pivoting.md" %} gcp-local-privilege-escalation-ssh-pivoting.md {% endcontent-ref %}

compute.instances.setMetadata

This permission gives the same privileges as the previous permission but over a specific instances instead to a whole project. The same exploits and limitations applies.

compute.instances.setIamPolicy

This kind of permission will allow you to grant yourself a role with the previous permissions and escalate privileges abusing them.

compute.instances.osLogin

If OSLogin is enabled in the instance, with this permission you can just run gcloud compute ssh [INSTANCE] and connect to the instance. You won't have root privs inside the instance.

compute.instances.osAdminLogin

If OSLogin is enabled in the instance, with this permission you can just run gcloud compute ssh [INSTANCE] and connect to the instance. You will have root privs inside the instance.

container

container.clusters.get

This permission allows to gather credentials for the Kubernetes cluster using something like:

gcloud container clusters get-credentials <cluster_name> --zone <zone>

Without extra permissions, the credentials are pretty basic as you can just list some resource, but hey are useful to find miss-configurations in the environment.

{% hint style="info" %} Note that kubernetes clusters might be configured to be private, that will disallow that access to the Kube-API server from the Internet. {% endhint %}

container.clusters.getCredentials

Apparently this permission might be useful to gather auth credentials (basic auth method isn't supported anymore by GKE if you use the latest GKE versions).

container.roles.escalate/container.clusterRoles.escalate

Kubernetes by default prevents principals from being able to create or update Roles and ClusterRoles with more permissions that the ones the principal has. However, a GCP principal with that permissions will be able to create/update Roles/ClusterRoles with more permissions that ones he held, effectively bypassing the Kubernetes protection against this behaviour.

container.roles.create and/or container.roles.update OR container.clusterRoles.create and/or container.clusterRoles.update respectively are also necessary to perform those privilege escalation actions.\

container.roles.bind/container.clusterRoles.bind

Kubernetes by default prevents principals from being able to create or update RoleBindings and ClusterRoleBindings to give more permissions that the ones the principal has. However, a GCP principal with that permissions will be able to create/update RolesBindings/ClusterRolesBindings with more permissions that ones he has, effectively bypassing the Kubernetes protection against this behaviour.

container.roleBindings.create and/or container.roleBindings.update OR container.clusterRoleBindings.create and/or container.clusterRoleBindings.update respectively are also necessary to perform those privilege escalation actions.

container.cronJobs.create, container.cronJobs.update container.daemonSets.create, container.daemonSets.update container.deployments.create, container.deployments.update container.jobs.create, container.jobs.update container.pods.create, container.pods.update container.replicaSets.create, container.replicaSets.update container.replicationControllers.create, container.replicationControllers.update container.scheduledJobs.create, container.scheduledJobs.update container.statefulSets.create, container.statefulSets.update

All these permissions are going to allow you to create or update a resource where you can define a pod. Defining a pod you can specify the SA that is going to be attached and the image that is going to be run, therefore you can run an image that is going to exfiltrate the token of the SA to your server allowing you to escalate to any service account.
For more information check:

{% content-ref url="../../pentesting-kubernetes/abusing-roles-clusterroles-in-kubernetes/" %} abusing-roles-clusterroles-in-kubernetes {% endcontent-ref %}

As we are in a GCP environment, you will also be able to get the nodepool GCP SA from the metadata service and escalate privileges in GCP (by default the compute SA is used).

container.secrets.get, container.secrets.list

As explained in this page, with these permissions you can read the tokens of all the SAs of kubernetes, so you can escalate to them.

container.pods.exec

With this permission you will be able to exec into pods, which gives you access to all the Kubernetes SAs running in pods to escalate privileges within K8s, but also you will be able to steal the GCP Service Account of the NodePool, escalating privileges in GCP.

container.pods.portForward

As explained in this page, with these permissions you can access local services running in pods that might allow you to escalate privileges in Kubernetes (and in GCP if somehow you manage to talk to the metadata service).

container.serviceAccounts.createToken

Because of the name of the permission, it looks like that it will allow you to generate tokens of the K8s Service Accounts, so you will be able to privesc to any SA inside Kubernetes. However, I couldn't find any API endpoint to use it, so let me know if you find it.

container.mutatingWebhookConfigurations.create, container.mutatingWebhookConfigurations.update

These permissions might allow you to escalate privileges in Kubernetes, but more probably, you could abuse them to persist in the cluster.
For more information follow this link.

storage

storage.hmacKeys.create

There is a feature of Cloud Storage, “interoperability”, that provides a way for Cloud Storage to interact with storage offerings from other cloud providers, like AWS S3. As part of that, there are HMAC keys that can be created for both Service Accounts and regular users. We can escalate Cloud Storage permissions by creating an HMAC key for a higher-privileged Service Account.

HMAC keys belonging to your user cannot be accessed through the API and must be accessed through the web console, but what’s nice is that both the access key and secret key are available at any point. This means we could take an existing pair and store them for backup access to the account. HMAC keys belonging to Service Accounts can be accessed through the API, but after creation, you are not able to see the access key and secret again.

The exploit script for this method can be found here.

storage.objects.get

This permission allows you to download files stored inside Gcp Storage. This will potentially allow you to escalate privileges because in some occasions sensitive information is saved there. Moreover, some Gcp services stores their information in buckets:

  • GCP Composer: When you create a Composer Environment the code of all the DAGs will be saved inside a bucket. These tasks might contain interesting information inside of their code.
  • GCR (Container Registry): The image of the containers are stored inside buckets, which means that if you can read the buckets you will be able to download the images and search for leaks and/or source code.

storage.objects.create, storage.objects.delete

In order to create a new object inside a bucket you need storage.objects.create and, according to the docs, you need also storage.objects.delete to modify an existent object.

A very common exploitation of buckets where you can write in cloud is in case the bucket is saving web server files, you might be able to store new code that will be used by the web application.

Moreover, several GCP services also store code inside buckets that later is executed:

  • GCP Composer: The DAG code is stored in GCP Storage. This code is later executed inside the K8s environment used by composer, and has also access to a GCP SA. Therefore, modifying this code you might be able to get inside the composer k8s env and steal the token of the GCP SA used.
  • GCR (Container Registry): The container images are stored inside buckets. So if you have write access over them, you could modify the images and execute your own code whenever that container is used.
    • The bucket used by GCR will have an URL similar to gs://<eu/usa/asia/nothing>.artifacts.<project>.appspot.com (The top level subdomains are specified here).

storage.objects.setIamPolicy

You can give you permission to abuse any of the previous scenarios of this section.

storage.objects Write permission

If you can modify or add objects in buckets you might be able to escalate your privileges to other resources that are using the bucket to store code that they execute.

Composer

Composer is Apache Airflow managed inside GCP. It has several interesting features:

  • It runs inside a GKE cluster, so the SA the cluster uses is accesible by the code running inside Composer
  • It stores the code in a bucket, therefore, anyone with write access over that bucket is going to be able change/add a DGA code (the code Apache Airflow will execute)
    Then, if you have write access over the bucket Composer is using to store the code you can privesc to the SA running in the GKE cluster.

References

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