According to guidance from Kaseya, the key is shifting focus from the inbox to the broader identity and endpoint landscape. Once a phishing email bypasses filtering, it usually triggers a chain of activity that leaves traces. Monitoring this activity is critical.

To effectively detect and contain these attacks, MSPs should focus on the following areas:

• Identity monitoring: Watch for abnormal authentication patterns, such as impossible travel, new device enrollments, or unusual MFA fatigue attempts. Attackers often use stolen credentials to access cloud apps.
• Email activity analysis: Look for post-delivery anomalies like mailbox rule creation, automatic forwarding to external addresses, or unexpected replies to internal threads. These are classic signs of a compromised account.
• Endpoint behavior: Track for suspicious processes spawned from email clients, unusual PowerShell usage, or the staging of files in temporary directories. These often indicate the execution of a payload.
• Cross-referencing signals: The real power lies in correlating a suspicious email with subsequent login attempts or file access patterns. A single alert might be false positive, but a chain of events is a strong indicator of compromise.

The threat isn't just the initial click—it's what happens afterward. Since filters will never be perfect, continuous visibility into user behavior and endpoint telemetry provides the last line of defense. By adopting this layered monitoring approach, MSPs can contain threats that would otherwise linger undetected in the environment.

Source: BleepingComputer