All too often, my baseVISION (IR) colleagues and I find compromised cloud accounts where many security ‘signals’ were missed—both from a prevention and detection perspective. In this blog post, I want to share some motivation and tips to help you adopt Entra ID Protection risk-based Conditional Access policies to increase your tenant’s security posture, and ensure you don’t miss the next obvious account breach.
Real-world motivation # Anyone who has seen an AiTM campaign in the wild will probably notice the following details from the Entra ID sign-in logs of a compromised account:
ResourceDisplayName: OfficeHome UserAgent: axios/1.13.2 The problem? Even though Entra ID Protection flagged the sign-in as ‘High’ risk, the user could still sign in because MFA automatically remediated the sign-in risk (userPassedMfaDrivenByRiskBasedPolicy).
The bummer? # The environment had a Conditional Access policy in place that would have blocked users with high sign-in risk, but the policy was only in report-only mode, so the user could sign in without any issues.
Recently I observed an interesting behavior after setting up a Microsoft Booking page. After creating the booking page, I suddenly got an e-mail to an automatically created mail alias with the same name as the booking page. This made me curious and I wanted to understand the behavior behind this, and if this could be abused by attackers to impersonate users in Exchange online. In this blog post, I want to share my findings and some tips on how to detect and prevent this kind of abuse in your environment.
Microsoft Booking # Microsoft describes the Bookings capabilities as part of Microsoft 365:
“A simpler way to organize schedules and manage appointments.”
Booking pages can be either of type ‘personal’ or ‘shared’:
Personal booking pages provide a handy option for users to create their own booking page, which is automatically linked to their calendar and allows others to book appointments with them. This is a great feature for users who want to share their availability and allow others to easily schedule meetings.
The shared booking pages allow teams to provide a booking experience for services hosted by a team and come with a special mailbox and calendar.
With the Unified Security Operations Platform (USOP), Microsoft introduces Unified Detections - a single detection framework spanning both Sentinel and Defender XDR data. Pair this with native Sentinel Data Lake ingestion for XDR tables, and you have a compelling cost-optimization story. But is it ready for prime time? Let’s dive into the capabilities, current limitations, and what it means for your detection strategy.
Architecture Overview # Previous Detection Architecture # In the ‘previous’ architecture, detections were created and managed separately for Microsoft Sentinel and Microsoft Defender XDR. This often led to overhead in terms of ‘where to create the detection’. Let’s take the use-case of IoC (Indicators of Compromise) based detections. Previously, if a security team wanted to create a detection based on IoCs imported via TAXII into Sentinel and the DeviceNetworkEvents table, they would need to ingest the DeviceNetworkEvents data into Sentinel as well and create the detection rule there. Furthermore, many MSSPs leveraged this pattern to create custom detections for their customers across Defender Advanced Hunting Data.
As part of the USOP onboarding, the following effects come into play, marked with an asterisk above: