Unmasking the Power and Perils of App Consent in Microsoft Graph & Entra ID

The Double-Edged Sword of Modern Authentication

In the ever-evolving landscape of cybersecurity, few topics are as crucial and potentially dangerous as App Consent and Microsoft Graph. As organizations increasingly rely on cloud-based services and APIs, understanding these concepts is no longer optional—it's a necessity for any cybersecurity professional worth their salt.

This blog post will take you on a journey through the intricate world of App Consent and Microsoft Graph, revealing both their immense power and hidden dangers. We'll explore how these technologies work, why they're important, and most critically, how they can be exploited by malicious actors. By the end of this post, you'll have a comprehensive understanding of the risks and the tools to mitigate them effectively.

The Gateway to Your Data

App Consent is a fundamental concept in modern authentication frameworks like Entra ID (formerly known as Azure Active Directory, A.K.A. Azure AD) . It allows third-party applications to request permissions to access user data and perform actions on behalf of users. While this enables powerful integrations and seamless user experiences, it also opens up potential security vulnerabilities if not properly managed.

Key Points About App Consent

By default, all users can access third-party applications, both verified and unverified.
Administrators can restrict this access, but existing consents aren't automatically revoked.
Global admins can inadvertently grant consent for the entire organization, potentially exposing all users' data.

Types of Consent

User Consent: The application works on behalf of the individual user.
Application Consent: The application can be granted full access to the organization, affecting all users.

The danger lies in users (or even administrators) granting excessive permissions without fully understanding the implications. A seemingly innocuous app could request access to read emails, calendars, and files—a goldmine for potential attackers.

One API to Rule Them All

Microsoft Graph is rapidly becoming the de facto API for interacting with Microsoft 365 services. It provides a unified endpoint for accessing data across various Microsoft cloud services, including Entra ID (formerly Azure AD), Exchange Online, SharePoint, and Teams.

Why Microsoft Graph Matters

Simplifies development by providing a single API for multiple services
Enables powerful integrations and automation capabilities
Offers granular permission scopes for fine-tuned access control

However, the power of Microsoft Graph also makes it an attractive target for attackers. With the right permissions, a malicious application could potentially access sensitive data across an entire organization.

The Anatomy of an App Consent Phishing Attack

Now that we understand the basics, let's dive into how cybercriminals exploit App Consent and Microsoft Graph to gain unauthorized access to organizations.

Steps in a Typical Attack

Attacker registers a multi-tenant application in their Entra ID (formerly Azure AD) tenant
A phishing email is sent to target users with a malicious link
User clicks the link and is presented with a legitimate Microsoft login page
After login, the user sees an app consent prompt for the malicious application
If the user grants consent, the attacker gains access to the specified resources
For example, once consent is granted, attacker uses the Microsoft Graph API to access the user's mailbox
They then search for sensitive information in email attachments, such as API keys, Slack Tokens, SSH keys, and more.
They then leverage these keys, to gain access to other systems

The key here is that once consent is granted, the attacker doesn't need the user's credentials to access their data. They can use the obtained access token to make API calls to Microsoft Graph, potentially reading emails, downloading attachments, or even modifying Entra ID (formerly known as Azure AD) settings.

Mitigating the Risks with Best Practices

Given the potential dangers of App Consent attacks, it's crucial to implement strong security measures. Here are some best practices to consider:

Implement strict app consent policies, limiting who can consent to applications
Regularly audit and review consented applications in your Entra ID tenant
Educate users about the risks of granting permissions to unknown applications
Use Entra ID Conditional Access policies to enforce additional security measures
Implement a process for vetting and approving third-party applications
Monitor for suspicious application consent grants using Entra ID logs and alerts

Vigilance in the Age of Cloud APIs

App Consent and Microsoft Graph represent a powerful set of technologies that enable modern, integrated cloud experiences. However, they also introduce new attack vectors that cybersecurity professionals must be prepared to address.

By understanding how these technologies work and how they can be exploited, you're better equipped to protect your organization from sophisticated phishing attacks and unauthorized access. Remember, in the world of cybersecurity, knowledge is not just power—it's your first line of defense.

Stay vigilant, keep learning, and never underestimate the creativity of potential attackers. The security of your organization depends on it!