On January 19, 2024, Microsoft disclosed a major security incident in which the email of Microsoft senior executives and other staff were accessed by Midnight Blizzard a.k.a Cozy Bear, a nation-state threat actor affiliated with Russia. Microsoft determined that the actor got initial access using password spray to compromise a legacy non-production test tenant account in Microsoft Entra ID (formerly Azure AD). The actor then moved laterally using the excessive permissions granted to that test account to access the email of Microsoft employees.

Password spray is a surprisingly simple and effective technique we’ve written about before. In a password spray attack, an attacker tries to login to a lot of accounts using a few probable passwords, with the hope that at least one account is using a weak password.

In this real-world external pentest, we’ll show NodeZero conducting a password spray attack against Microsoft Entra ID to get initial access to a client’s tenant account, similar to what Midnight Blizzard did. From there NodeZero detects that multi-factor authentication is disabled and breaks into the email of the compromised user.

A Real World Example

In this example, a client conducted an external pentest using NodeZero. NodeZero ran from Horizon3.ai’s cloud environment and was not provided any credentials.

Configuring an External Pentest for Password Spray

When defining the assets in scope for this pentest, the client provided NodeZero a list of company-owned domains. NodeZero uses these domains to enumerate Azure tenants that belong to the client.

In the Attack Configuration for the pentest, the MS Entra (Azure AD) Password Spray flag was also enabled. This is on by default.

To avoid locking out accounts, NodeZero only attempts three passwords an hour. A duration of time can be set for how long the pentest runs, in order to get in more password spray attempts.

Attack Path

Here are the steps NodeZero took in this test to get to business email compromise:

1. NodeZero used the provided domains to discover a Microsoft Entra tenant associated with the client.
2. NodeZero used open source intelligence (OSINT) to discover potential usernames associated with the client.
3. NodeZero verified which users are actual users belonging to the client’s tenant.
4. NodeZero sprayed a highly probable password against all verified users. One of the users hit!
5. NodeZero then discovered that MFA was disabled for the user. NodeZero logged into the user’s account and acquired an Azure access and refresh token.
6. NodeZero then accessed the user’s Microsoft365 inbox.

The full attack path is shown below:

Takeaways

It took NodeZero less than 10 minutes to execute this attack path leading to business email compromise, starting with no privileges in the form of credentials or network access. This attack was performed autonomously with no human assistance or prior scripting.

The impact of business email compromise is huge. Not only can attackers access potentially sensitive data, they can use the compromised account to conduct lateral phishing attacks and further escalate privileges.

Microsoft has been rolling out MFA for all its tenants, but in practice we’ve seen that there have been gaps in this rollout, just as Microsoft experienced with its own legacy test tenant. The application of MFA also depends on how the tenant is configured. Use NodeZero to verify your true security posture!