Design Flaw in Domain-Wide Delegation Could Leave Google Workspace Vulnerable for Takeover, Says Cybersecurity Company Hunters

Boston, Massachusetts, November 28th, 2023, Cyberwire

A severe design flaw in Google Workspace’s domain-wide delegation feature discovered by threat hunting experts from Hunters’ Team Axon, can allow attackers to misuse existing delegations, enabling privilege escalation and unauthorized access to Workspace APIs without Super Admin privileges. Such exploitation could result in theft of emails from Gmail, data exfiltration from Google Drive, or other unauthorized actions within Google Workspace APIs on all of the identities in the target domain. Hunters has responsibly disclosed this to Google and worked closely with them prior to publishing this research. 

Domain-wide delegation permits a comprehensive delegation between Google Cloud Platform (GCP) identity objects and Google Workspace applications. In other words, it enables GCP identities to execute tasks on Google SaaS applications, such as Gmail, Google Calendar, Google Drive, and more, on behalf of other Workspace users.

The design flaw, which the team at Hunters has dubbed “DeleFriend,” allows potential attackers to manipulate existing delegations in GCP and Google Workspace without possessing the high-privilege Super Admin role on Workspace, which is essential for creating new delegations. Instead, with less privileged access to a target GCP project, they can create numerous JSON web tokens (JWTs) composed of different OAuth scopes, aiming to pinpoint successful combinations of private key pairs and authorized OAuth scopes which indicate that the service account has domain-wide delegation enabled. 

The root cause lies in the fact that the domain delegation configuration is determined by the service account resource identifier (OAuth ID), and not the specific private keys associated with the service account identity object. 

Additionally, no restrictions for fuzzing of JWT combinations were implemented on the API level, which does not restrict the option of enumerating numerous options for finding and taking over existing delegations.

This flaw poses a special risk due to potential impact described above and is amplified by the following:

• Long Life: By default, GCP Service account keys are created without an expiry date. This feature makes them ideal for establishing backdoors and ensuring long-term persistence.
• Easy to hide: The creation of new service account keys for existing IAMs or, alternatively, the setting of a delegation rule within the API authorization page is easy to conceal. This is because these pages typically host a wide array of legitimate entries, which are not examined thoroughly enough.
• Awareness: IT and Security departments may not always be cognizant of the domain-wide delegation feature. They might especially be unaware of its potential for malicious abuse.
• Hard to detect: Since delegated API calls are created on behalf of the target identity, the API calls will be logged with the victim details in the corresponding GWS audit logs. This makes it challenging to identify such activities. 

“The potential consequences of malicious actors misusing domain-wide delegation are severe. Instead of affecting just a single identity, as with individual OAuth consent, exploiting DWD with existing delegation can impact every identity within the Workspace domain,” says Yonatan Khanashvili of Hunters’ Team Axon.

The range of possible actions varies based on the OAuth scopes of the delegation. For instance, email theft from Gmail, data exfiltration from the drive, or monitor meetings from Google Calendar.

In order to execute the attack method, a particular GCP permission is needed on the target Service Accounts. However, Hunters observed that such permission is not an uncommon practice in organizations making this attack technique highly prevalent in organizations that don’t maintain a security posture in their GCP resources. “By adhering to best practices, and managing permissions and resources smartly, organizations can dramatically minimize the impact of the attack method” Khanashvili continued. 

Hunters has created a proof-of-concept tool (full details are included in the full research) to assist organizations in detecting DWD misconfigurations, increasing awareness, and reducing DeleFriend’s exploitation risks. Using this tool, red teams, pen testers, and security researchers can simulate attacks and locate vulnerable attack paths of GCP IAM users to existing delegations in their GCP Projects to evaluate (and then improve) the security risk and posture of their Workspace and GCP environments. 

Hunters’ Team Axon has also compiled comprehensive research that lays out exactly how the vulnerability works as well as recommendations for thorough threat hunting, detection techniques, and best practices for countering domain-wide delegation attacks.

Hunters responsibly reported DeleFriend to Google as part of Google’s “Bug Hunters” program in August, and are collaborating closely with Google’s security and product teams to explore appropriate mitigation strategies. Currently, Google has yet to resolve the design flaw.

Read the full research here, and follow Hunters’ Team Axon on Twitter.

About Hunters

Hunters delivers a Security Operations Center (SOC) Platform that reduces risk, complexity, and cost for security teams. A SIEM alternative, Hunters SOC Platform provides data ingestion, built-in and always up-to-date threat detection, and automated correlation and investigation capabilities, minimizing the time to understand and respond to real threats. Organizations like Booking.com, ChargePoint, Yext, Upwork and Cimpress leverage Hunters SOC Platform to empower their security teams. Hunters is backed by leading VCs and strategic investors including Stripes, YL Ventures, DTCP, Cisco Investments, Bessemer Venture Partners, U.S. Venture Partners (USVP), Microsoft’s venture fund M12, Blumberg Capital, Snowflake, Databricks, and Okta.

Contact

Yael Macias
yael@hunters.security