[update] Microsoft infrastructure abuse with suspicious patterns

[MSAdministrator]

Description

The modified rule significantly expands detection capabilities beyond the original version. While the original rule primarily relied on header analysis and a basic phone number regex pattern, the enhanced version adds three major improvements:

• specific indicator-of-compromise (IOC) strings like "CloudSync," "TenantHub," and known malicious phone numbers that have been observed in active campaigns
• sophisticated phone number detection using dual regex patterns that catch obfuscation techniques where attackers substitute letters (i, l, o) for numbers to evade simple pattern matching
• logo detection layer that flags messages when SPF/DMARC/DKIM checks fail while Microsoft branding is detected via machine learning.

The modified rule also adds "invites" as a suspicious sender local part and updates detection methods to include "Content analysis" and "Natural Language Understanding," transforming the rule from a primarily header-based detector into a comprehensive multi-signal analyzer that catches both infrastructure abuse and sophisticated social engineering tactics used in Microsoft-themed callback phishing campaigns.

Associated samples

• Sample

Associated hunts

• Hunt