Microsoft has announced significant security enhancements for Teams, introducing robust protections against malicious file types and dangerous URLs.
In a dual-pronged update, Microsoft will automatically block potentially dangerous executables and warn users about malicious URLs in chats and channels.
“Microsoft Teams now blocks messages containing weaponizable file types, such as executables, in chats and channels, increasing protection against malware and other file-based attacks,”
Microsoft said in a roadmap update.
“Microsoft Teams can now detect and warn users on malicious URLs sent in Teams chat and channels,” it added in a separate entry.
These security improvements represent Microsoft’s comprehensive and company-wide efforts to address fundamental vulnerabilities in its security posture, although some question why this update was not implemented sooner.
Microsoft’s Comprehensive Security Overhaul
The security update marks a shift in how Microsoft Teams handles potential threats, implementing automated detection and blocking mechanisms at the platform level.
Microsoft’s roadmap entries 499892 and 499893 detail that Teams will now scan both file attachments and embedded URLs for malicious content before they reach users.
Files containing executables can, once clicked, instruct a computer or platform to run a certain program, potentially downloading malware or Trojans. URLs can lead users to sites that deliver malware to their computers.
This proactive approach minimizes the human factor that has made Teams users vulnerable to social engineering attacks, where legitimate-looking attachments or URLs contain malicious payloads designed to compromise corporate networks.
Additionally, Microsoft announced in the Microsoft 365 Message Center that Teams now integrates with the Microsoft Defender for Office 365 Tenant Allow/Block List. This enables security administrators to block incoming communications (chats, channels, meetings, and calls) from blocked domains, automatically delete existing communications from users in blocked domains, and manage blocked external domains in Microsoft Teams via the Microsoft Defender portal.
Such control eliminates the ability for malicious files or URLs to remain within a system long after they are identified.
All features are due to roll out by late September 2025. Despite this seemingly imminent rollout, hackers have long exploited executables in Teams.
The Growing Threat Landscape in UC
Teams has become a prime target for sophisticated threat actors due to its central role in modern business communications.
Increasingly, more business-critical information is being shared on these platforms, yet its security is seen as a weak spot for gaining wider entry into company networks.
Cybersecurity researchers have documented increasingly creative attack methodologies that exploit the platform’s collaborative features.
Hacking group Storm-2372 has used a technique exploiting Microsoft’s OAuth 2.0 Device Authorization Grant flow through fake Teams meeting invitations.
This campaign, active since August 2024, has successfully targeted government agencies, NGOs, and critical infrastructure organizations across multiple continents, highlighting the global reach and sophistication of Teams-focused attacks.
Cybersecurity firm Check Point has observed malicious executable files used in Teams chats since 2022.
Therefore, many wonder why Microsoft has taken so long to address this security threat, given its wide recognition as a weakness.
The tech titan has recently stepped up efforts to improve its security, following several high-profile failures—including a $5 million pay cut for its CEO over the company’s inability to fend off cyberattacks.
Since then, Microsoft has launched its Secure Future Initiative, aimed at strengthening cloud security across its company and products.
How New Protections Address Critical Vulnerabilities
Microsoft’s automated file-blocking system directly counters malware distribution methods that have made Teams an effective attack vector, removing the user decision-making process that cybercriminals have exploited in countless campaigns.
By preventing dangerous executables from reaching users, the new protections eliminate the human element that has been the weakest link in Teams’ security architecture.
The URL scanning functionality addresses a critical gap in Teams security by providing real-time analysis of links shared in conversations. This capability is especially important since Storm-2372 and similar threat actors have relied on legitimate-looking links to redirect users to credential harvesting or malware distribution sites.
Integration with Microsoft’s broader security ecosystem ensures that Teams’ protections will benefit from expanded control over who can message users. This also helps align security policies between email and Teams interactions, closing potential gaps in organizational security.
Securing the Future of Business Communications
Microsoft’s comprehensive security overhaul for Teams represents long-overdue recognition that UC platforms are increasingly targeted with attacks using executables.
By implementing automated protections against malicious files and URLs, Microsoft acknowledges that user education alone is insufficient to defend against sophisticated social engineering attacks.
The integration of Teams security with Microsoft’s broader Defender ecosystem suggests a strategic shift toward treating UC as part of core security infrastructure, not merely a peripheral collaboration tool.
As remote work continues to reshape organizational communications, the security of platforms like Teams will become increasingly critical to overall enterprise cybersecurity.
