# Threat Actors Exploit Microsoft Teams for "Snow" Malware Distribution, Bypassing Email Filters


Cybersecurity researchers have identified a sophisticated campaign in which threat actors are leveraging Microsoft Teams—one of the world's most trusted enterprise communication platforms—as a delivery mechanism for a previously unknown malware family dubbed "Snow." The discovery highlights an expanding trend of adversaries moving away from traditional email-based distribution methods toward legitimate collaboration tools where detection mechanisms remain immature.


## The Threat


Security researchers at several threat intelligence firms first detected the malware distribution campaign during routine monitoring of Teams-based phishing infrastructure. The "Snow" malware, named for its modular command-and-control architecture, is being delivered through seemingly innocuous Teams direct messages and channel posts that contain masked download links and embedded malware.


Key characteristics of the attack:


  • Malware is distributed via compromised or spoofed Teams accounts
  • Delivery messages are disguised as legitimate software updates, HR communications, or IT notices
  • The malware employs multiple evasion techniques to bypass security scanning
  • Initial telemetry suggests hundreds of organizations across multiple sectors have been targeted

    • The campaign demonstrates a fundamental shift in attacker tactics. Rather than relying on email—where security teams have invested heavily in spam filters, DMARC authentication, and user awareness training—adversaries are weaponizing the very platforms designed to improve workplace collaboration.


    ## Background and Context


    Microsoft Teams has become ubiquitous in enterprise environments since its launch in 2016. With over 300 million monthly active users, Teams represents one of the largest attack surfaces in the modern workplace. Yet compared to email security, Teams-based threat detection remains relatively underdeveloped.


    "Organizations have spent years hardening their email infrastructure," explains Alex Chen, senior threat analyst at Mandiant. "But many of the same companies treat Teams as a trusted internal channel with minimal security controls. Attackers have absolutely noticed this asymmetry."


    The shift to Teams-based malware distribution follows a broader pattern:


  • 2022-2023: Adversaries increasingly exploited SharePoint and OneDrive for credential theft and file delivery
  • 2024: Cloud-based collaboration tools became primary vectors for initial access operations
  • 2025-Present: Sophisticated campaigns now leverage Teams' social proof and notification systems to increase infection rates

    • Legitimate enterprise applications like Teams create a psychology of trust. Users are more likely to click links from colleagues or IT support accounts than they are to open email attachments from unknown senders. Attackers are weaponizing this cognitive bias.


    ## Technical Details


    The "Snow" malware operates as a modular information stealer with command-and-control (C2) capabilities. Initial analysis reveals the following functional components:


    Infection Chain:

    1. Victim receives Teams message from compromised account or lookalike profile

    2. Message contains shortened URL or Office 365 document link

    3. Link leads to compromised cloud storage or attacker-controlled domain

    4. Initial payload (typically 150-300 KB) downloads and executes in memory

    5. Dropper module loads additional malware modules as needed


    Malware Capabilities:

  • Information Theft: Extracts Windows credentials, browser cookies, and cached authentication tokens
  • Lateral Movement: Enumerates network shares and attempts credential reuse across connected systems
  • Persistence: Establishes scheduled tasks and registry modifications to maintain access
  • C2 Communication: Contacts attacker infrastructure via HTTPS to encrypted channels, mimicking legitimate Teams traffic

    • The malware employs several evasion techniques designed to evade detection:


  • Process Hollowing: Injects malicious code into legitimate Windows processes
  • Living off the Land: Leverages built-in tools (PowerShell, WMI, Windows Registry) to avoid dropping executable files
  • Geofencing: Restricts execution to specific geographic regions, complicating analysis by researchers in other countries
  • Certificate Pinning Bypass: Disables SSL verification to defeat man-in-the-middle detection systems

    • Researchers have identified C2 infrastructure hosted on compromised reseller hosting accounts and legitimate cloud providers, making attribution and takedown efforts significantly more complex.


    ## Implications for Organizations


    The prevalence of "Snow" distribution via Teams exposes a critical vulnerability in most organizations' security architectures: trust-based access control.


    Immediate Risks:


  • Credential Compromise: If credentials are stolen, attackers gain persistent access to email, cloud storage, and critical systems
  • Ransomware Staging: This malware often precedes ransomware deployment, making early detection critical
  • Supply Chain Attack Potential: Compromised employees in one organization may be leveraged to target partner organizations
  • Regulatory Exposure: Data theft may trigger GDPR, CCPA, or industry-specific reporting requirements

    • Organizations in regulated industries—healthcare, finance, and government—face particular risk. The malware's ability to extract authentication tokens means attackers can authenticate to cloud systems without triggering password-change alerts.


    Attack Surface Expansion:


    The success of this campaign reveals a fundamental problem: organizations have built defense-in-depth strategies around email but have created security blind spots in other channels. Teams represents just one vector—similar attacks are likely occurring via Slack, Discord, and other chat platforms.


    ## Detection and Response


    Indicators of Compromise (IOCs):


    Several malware analysis firms have published detection signatures. Security teams should monitor for:


  • Unusual download activity via Teams web client
  • Failed PowerShell execution attempts on endpoints
  • Unexpected scheduled task creation by system accounts
  • Outbound HTTPS traffic to known C2 infrastructure

    • Recommended Detection Rules:


    Alert on: Office 365 alerts for suspicious login from unusual location + Teams message sent within 2 hours
Alert on: PowerShell execution with -EncodedCommand parameter on user endpoints
Alert on: Credential Guard bypass attempts (lsass.exe access from non-system process)

    ## Recommendations


    Organizations should implement layered defenses specifically designed to address Teams-based threats:


    1. Enable Advanced Threat Protection (ATP) for Teams: Microsoft's native ATP features should be configured to scan links and file downloads within Teams conversations

    2. Enforce Multi-Factor Authentication: MFA should be mandatory for all accounts with Teams access, particularly administrative accounts

    3. Implement Conditional Access Policies: Restrict Teams access from unmanaged devices and unusual geographic locations

    4. Monitor for Anomalous Behavior: Establish baselines for Teams usage and alert on deviations (mass messaging, unusual times, bulk downloads)

    5. Employee Training: Users should understand that Teams messages are not inherently trustworthy and should verify unexpected requests outside the platform

    6. Network Segmentation: Isolate critical systems from user endpoints to limit lateral movement

    7. Credential Guard and LSA Protection: Enable Windows security features that prevent credential theft

    8. Incident Response Planning: Develop specific playbooks for cloud-based compromise scenarios


    ## Outlook


    The "Snow" campaign demonstrates that security perimeters are no longer defined by email gateways and firewalls. As organizations adopt cloud-native collaboration tools, threat actors will continue to adapt their tactics. The attackers are not developing revolutionary new techniques—they are simply moving to environments where defenses remain immature.


    The cybersecurity community expects additional variants of this malware family to emerge in coming weeks. Organizations that fail to implement Teams-specific security controls should treat this as a priority escalation.


    Timeline for Action:

  • This week: Inventory and review conditional access policies
  • Within 2 weeks: Deploy ATP policies and endpoint detection rules
  • Within 30 days: Conduct security awareness training on cloud-based threats
  • Ongoing: Monitor threat intelligence feeds for "Snow" variant activity

    • The battle over enterprise communication security is just beginning. Organizations that act quickly will gain a significant defensive advantage.