# GCP - Cloud Build Unauthenticated Enum

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## Cloud Build

For more information about Cloud Build check:

{% content-ref url="../gcp-services/gcp-cloud-build-enum.md" %}
[gcp-cloud-build-enum.md](../gcp-services/gcp-cloud-build-enum.md)
{% endcontent-ref %}

### cloudbuild.yml

If you compromise write access over a repository containing a file named **`cloudbuild.yml`**, you could **backdoor** this file, which specifies the **commands that are going to be executed** inside a Cloud Build and exfiltrate the secrets, compromise what is done and also compromise the **Cloud Build service account.**

{% hint style="info" %}
Note that GCP has the option to allow administrators to control the execution of build systems from external PRs via "Comment Control". Comment Control is a feature where collaborators/project owners **need to comment “/gcbrun” to trigger the build** against the PR and using this feature inherently prevents anyone on the internet from triggering your build systems.
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For some related information you could check the page about how to attack Github Actions (similar to this):

{% content-ref url="../../../pentesting-ci-cd/github-security/abusing-github-actions/" %}
[abusing-github-actions](../../../pentesting-ci-cd/github-security/abusing-github-actions/)
{% endcontent-ref %}

### PR Approvals

When the trigger is PR because **anyone can perform PRs to public repositories** it would be very dangerous to just **allow the execution of the trigger with any PR**. Therefore, by default, the execution will only be **automatic for owners and collaborators**, and in order to execute the trigger with other users PRs an owner or collaborator must comment `/gcbrun`.

<figure><img src="../../../.gitbook/assets/image (339).png" alt="" width="563"><figcaption></figcaption></figure>

{% hint style="danger" %}
Therefore, is this is set to **`Not required`**, an attacker could perform a **PR to the branch** that will trigger the execution adding the malicious code execution to the **`cloudbuild.yml`** file and compromise the cloudbuild execution (note that cloudbuild will download the code FROM the PR, so it will execute the malicious **`cloudbuild.yml`**).
{% endhint %}

Moreover, it's easy to see if some cloudbuild execution needs to be performed when you send a PR because it appears in Github:

<figure><img src="../../../.gitbook/assets/image (340).png" alt=""><figcaption></figcaption></figure>

{% hint style="warning" %}
Then, even if the cloudbuild is not executed the attacker will be able to see the **project name of a GCP project** that belongs to the company.
{% endhint %}

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Learn & practice AWS Hacking:<img src="../../../.gitbook/assets/image (1) (1) (1) (1).png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="../../../.gitbook/assets/image (1) (1) (1) (1).png" alt="" data-size="line">\
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{% endhint %}