Sophisticated threat actors like APT29 (UNC2452) have demonstrated that there is no formal security boundary between on-premises networks and cloud services. Once inside an environment, these groups utilize advanced techniques—such as "Golden SAML" and Azure AD backdoors—to bypass Multi-Factor Authentication (MFA) and maintain persistent access to Microsoft 365 data even after the initial entry point is secured.
We are sharing this definitive white paper from Mandiant, which outlines the specific tactics, techniques, and procedures (TTPs) used by APT29. It provides a battle-tested roadmap for remediation, ensuring you can effectively eradicate the threat actor and harden your tenant against re-compromise.
What You Will Learn: This guide goes beyond standard best practices, offering deep technical remediation steps for complex attack vectors, including:
- Defending Against Golden SAML: Understand how attackers steal AD FS token-signing certificates to forge authentication tokens, and learn the critical "double-tap" rotation strategy required to invalidate them.
- Detecting Azure AD Backdoors: Learn to identify illicit "Federated Trusts" and hijacked Service Principals where attackers add rogue credentials to bypass authentication controls.
- Mailbox Persistence Techniques: Explore how attackers use Application Impersonation and modified Mailbox Folder Permissions to silently exfiltrate email without triggering standard login alerts.
- Supply Chain & CSP Risk: Discover how threat actors abuse Delegated Administration privileges to pivot from compromised Cloud Service Providers (CSPs) into downstream customer tenants.
- Hardening & Auditing: Access specific PowerShell scripts (including the Azure AD Investigator tool) to audit for "MailItemsAccessed" events, verify "Purview Audit" licensing, and detect attempts to disable logging features.
Download the Full White Paper Whether you are responding to an active intrusion or proactively hardening your identity infrastructure, this document provides the granular command-line instructions and architectural changes needed to defend your Microsoft 365 environment. Download "Remediation and Hardening Strategies for Microsoft 365 to Defend Against APT29" for the complete checklist.