Microsoft Teams Flaw in Guest Chat Exposes Users to Malware Attacks

Microsoft Teams has become the main tool for communication in businesses globally. Due to this, security teams spend a lot of time and money on protection services like Microsoft Defender for Office 365 to guard against dangers like phishing emails, malicious links, and malware.

However, new research from the security firm Ontinue, released on Wednesday, November 26, shows a huge security flaw in the standard setup of Microsoft Teams collaboration with outside partners, known as B2B Guest Access, which lets attackers entirely bypass a company’s Microsoft Defender protections.

Who Controls Your Security as a Guest?

The problem isn’t actually a software bug in Teams; it’s about the way security is managed when employees work with external groups. Ontinue’s blog post makes it clear; when your staff accepts an outside invitation and joins another company’s chat, their security is no longer determined by their home organisation. Instead, the research found that…