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Google Cloud Platform (GCP) Privilege Escalation Vulnerability in GCP Composer

Medium
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Synopsis

Tenable Research has discovered a privilege escalation vulnerability affecting Google Cloud Composer. This vulnerability allows an identity with the composer.environments.update permission to escalate privileges to the default Cloud Build service account, which holds elevated permissions within Google Cloud environments.

 

The vulnerability exploits the process of adding custom PyPI packages to Cloud Composer. During this process, a Cloud Build instance is automatically initiated by the Composer service account, which attaches the default Cloud Build service account with elevated permissions. By uploading a malicious PyPI package, attackers can inject code that executes during the build process, exfiltrating the token of the Cloud Build service account from its metadata.

This attack technique was previously reported in Google Cloud Functions by Tenable and was dubbed ConfusedFunction, but a variant of the vulnerability persists in Cloud Composer.

Solution

Previously, during update operations performing PyPI modules installation, Composer used the Cloud Build service account (which might have had broader permissions than the user performing the operation). After implementing the fix, Composer will stop using Cloud Build service account and instead will use Composer environment service account for performing PyPI module installations.

 

This has been rolled out to new Composer instances already and existing instances should be updated to exhibit this behavior in April 2025.

 

In addition, this report led to several updates to our Composer documentation, such as to the sections on Access Control, Installing Python Dependencies, and Accessing the Airflow CLI.

This fix has been rolled out to new Composer instances already (rel. notes) and existing instances should be updated to exhibit this behavior in April (rel. notes).

Additional References

https://cloud.google.com/composer/docs/composer-2/access-control#:~:text=The%20composer.environments,with%20such%20code
https://cloud.google.com/composer/docs/composer-2/install-python-dependencies#:~:text=Important%3A%20When,Access%20control
https://cloud.google.com/composer/docs/composer-3/access-airflow-cli#:~:text=Caution%3A%20Users%20with%20the%20composer.environment.executeairflowcommand%20permission%20can%20execute%20Python%20code%20available%20to%20Airflow%20components%20on%20behalf%20of%20the%20environment%27s%20service%20account.%20For%20more%20information%2C%20see%20Access%20control

Disclosure Timeline

October 19, 2024 - Tenable reported the finding to Google
October 19, 2024 - Google triages the report
October 28, 2024 - Google confirmed the finding
November 6, 2024 - Google asks for clarification on the disclosure date
November 6, 2024 - Tenable provides clarification
November 18, 2024 - Tenable asks for updates on the finding
November 19, 2024 - Google still addresses the reported issue
December 9, 2024 - Tenable asks Google for an update on the report
December 10, 2024 - Google has no updates yet
December 23, 2024 - Tenable asks for updates on the report, no updates yet
January 9, 2025 - Google updates that the product team went back and forth on what changes needed to be made and asks for a blog draft
January 26, 2025 - Tenable asks for updates on the report and says the draft is not ready yet
January 29, 2025 - Google says that the fix for this issue was scheduled to be released shortly but has been delayed and asks for the blog draft status
January 30, 2025 - The permanent fix is already available for newly created Composer environments and the permanent fix will be applied to existing Composer environments in the middle of April
February 4, 2025 - Tenable informs Google of the end of the disclosure period and willing to extend the disclosure period by 2 additional weeks to allow a full fix
February 6, 2025 - Google acknowledges and says the extension is not necessary, new Composer instances are fixed, but existing Composers are still waiting for a fix
February 9, 2025 - Tenable thanks Google for the updates and fix, and updates Google that they plan to issue an advisory and will share the draft soon
February 10, 2025 - Tenable asks Google for final details on the fix and solution deployed
February 13, 2025 - Google updates Tenable with the fix details
February 17, 2025 - Tenable shares the TRA draft with Google

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

Risk Information

Tenable Advisory ID: TRA-2025-03
Credit:
Liv Matan
Affected Products:
GCP Composer
Risk Factor:
Medium

Advisory Timeline

February 18, 2025 - Initial release.
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