CISA and FBI Release Cybersecurity Advisory on Enhanced Monitoring to Detect APT Activity Targeting Outlook Online

The Cybersecurity and Infrastructure Security Agency (CISA) and Federal Bureau of Investigation (FBI) have released a joint Cybersecurity Advisory (CSA), Enhanced Monitoring to Detect APT Activity Targeting Outlook Online, to provide guidance to agencies and critical infrastructure organizations on enhancing monitoring in Microsoft Exchange Online environments. 

In June 2023, a Federal Civilian Executive Branch (FCEB) agency observed unexpected events in Microsoft 365 (M365) audit logs. After reporting the incident to Microsoft, network defenders deemed the activity malicious. As a response, Microsoft released this guidance: 

• Microsoft: Microsoft Mitigates China-based Threat Actor Storm-0558 Targeting of Customer Email
• Microsoft: Mitigation for China-Based Threat Actor Activity
• Microsoft: Analysis of Storm-0558 Techniques for Unauthorized Email Access

The goal of this CSA is to enhance organizational cybersecurity posture and position organizations to detect similar malicious activity via implementing the listed logging recommendations. 

Organizations that identify suspicious, anomalous activity should contact Microsoft for proceeding with mitigation actions due to the cloud-based infrastructure affected, as well as report to CISA and the FBI. For mitigations that are classified as preventative measures (e.g., steps to take to reduce the risk of network categorized exposure), CISA and FBI strongly encourage that FCEB agencies and critical infrastructure organizations ensure audit logging is enabled. Note: See CISA’s Microsoft Exchange Online Microsoft 365 Minimum Viable Secure Configuration Baselines. These minimum viable secure configuration baselines are part of CISA’s Secure Cloud Business Applications (SCuBA) project. 

For additional information and guidance, CISA and the FBI encourage network defenders to take the measures listed in this CSA to reduce the likelihood of similar activity and posture for detection.