Understanding Azure AD User Enumeration Techniques
Attackers often seek to identify valid user accounts within an Azure Active Directory (Azure AD) environment to facilitate further attacks, such as password spraying, phishing, or lateral movement. Azure AD, by design, can expose certain information through public endpoints or misconfigurations, enabling such enumeration.
Common Techniques for Azure AD User Enumeration
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Unauthenticated Email Address Enumeration
Attackers can validate the existence of email addresses associated with an Azure AD tenant by leveraging public endpoints. Tools like CredMaster and Quiet Riot automate this process by testing a list of potential email addresses against known patterns or APIs, identifying valid accounts without requiring authentication.
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Exploiting Default OneDrive URLs
Each user in Azure AD is provisioned with a default OneDrive URL upon activation. Attackers can enumerate these URLs to identify valid users. Tools such as Nyxgeek have demonstrated this technique, highlighting the risks associated with default configurations.
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Guest Access Misconfigurations
In some Azure AD tenants, guest users may have permissions that allow them to enumerate users, groups, and applications. By exploiting these permissions, attackers can gather information about the organization's structure and potential targets.
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PowerShell Scripts for Automated Enumeration
Scripts like the one demonstrated by Daniel Chronlund utilize PowerShell to automate the process of checking the existence of user accounts. These scripts can be configured to test multiple usernames efficiently, aiding attackers in identifying valid accounts.
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Password Spraying Using Validated Emails
Once valid email addresses are identified, attackers may employ password spraying techniques, attempting to authenticate using common passwords across multiple accounts. This method reduces the risk of account lockouts and increases the likelihood of successful unauthorized access.
Mitigation Strategies
To reduce the risk of user enumeration in Azure AD:
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Implement Conditional Access Policies: Restrict access to sensitive resources based on conditions such as user location, device compliance, and risk levels.
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Enforce Multi-Factor Authentication (MFA): Require MFA for all users to add an additional layer of security beyond just usernames and passwords.
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Configure Guest Access Permissions Carefully: Review and adjust guest user permissions to limit their ability to enumerate directory information.
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Monitor and Respond to Suspicious Activities: Utilize tools like Microsoft Defender for Identity to detect and respond to anomalous login attempts and other suspicious activities.
Understanding the techniques attackers use to enumerate Azure AD users is crucial for implementing effective security measures. By proactively configuring Azure AD settings, monitoring access patterns, and educating users, organizations can significantly reduce the risk of unauthorized access and potential breaches.
