As Microsoft continues to grow in popularity, its collaboration platform, Microsoft Teams, has become a hub for business communication and productivity. However, with its increasing adoption, Microsoft Teams has also become a prime target for threat actors seeking to exploit vulnerabilities in the platform for malicious purposes. In a recent warning, Microsoft highlighted the alarming trend of external Microsoft Teams collaboration being abused by hackers to impersonate IT or helpdesk staff, tricking employees into providing remote access for data theft purposes.
Microsoft Teams Abused: A Growing Threat
Threat actors are increasingly using Microsoft Teams to launch targeted attacks on businesses, exploiting the platform’s features to gain a foothold in the network and exfiltrate sensitive data. These attacks often begin with a malicious message sent to targets via an external Teams chat, where the attacker poses as a member of the company’s IT staff, claiming to address an account issue or perform a security update.
The Attack Chain: A Step-by-Step Analysis
Microsoft has documented a nine-stage attack chain that hackers use to exploit Microsoft Teams for their nefarious purposes. This attack chain begins with the threat actor contacting the target via an external Teams chat, posing as a member of the company’s IT staff. The goal is to convince the target to grant remote assistance access, which gives the attacker direct control of the employee’s machine.
Once the attacker gains access, they perform quick reconnaissance using Command Prompt and PowerShell, checking privileges, domain membership, and network reachability to evaluate the potential for lateral movement. This is followed by the dropping of a small payload bundle in user-writable locations such as ProgramData and the execution of the malicious code through a trusted, signed application (e.g., Autodesk, Adobe Acrobat/Reader, Windows Error Reporting, data loss prevention software) via DLL side-loading.
The HTTPS-based communication to the command-and-control (C2) established this way blends into normal outbound traffic, making it more difficult to detect. With the infection established and persistence secured via Windows Registry modifications, the attacker proceeds to abuse Windows Remote Management (WinRM) to move laterally across the network, targeting domain-joined systems and high-value assets such as domain controllers.
Abuse of Legitimate Tools
One of the key aspects of these attacks is the abuse of legitimate tools and protocols. Hackers use commercial remote management software, such as Quick Assist, and the Rclone utility to transfer files to an external cloud storage service. This abuse of legitimate tools makes it challenging to discern follow-on malicious activity from normal operations, as the attackers blend into routine IT support activity throughout the intrusion lifecycle.
Targeted Data Exfiltration
The attackers employ filters to focus on valuable information, reduce transfer volume, and improve operational stealth. They use Rclone or similar tools to collect and exfiltrate sensitive data to external cloud storage points, often targeting domain-joined systems and high-value assets. This targeted approach enables the attackers to exfiltrate sensitive data without being detected.
Microsoft notes that this exfiltration step is rather targeted, employing filters to focus only on valuable information, reduce transfer volume, and improve operational stealth. This level of sophistication makes it increasingly difficult for security teams to detect and prevent these types of attacks.
Microsoft’s Recommendations
Microsoft has issued several recommendations to help businesses prevent these types of attacks. Firstly, the company advises users to treat external Teams contacts as untrusted by default. This means that users should be cautious when interacting with external contacts, especially if they are requesting remote assistance or access to sensitive data.
Secondly, Microsoft recommends that administrators restrict or closely monitor remote assistance tools, such as Quick Assist. This can help prevent attackers from gaining access to employee machines and exploiting them for malicious purposes.
Lastly, Microsoft suggests limiting WinRM usage to controlled systems. This can help prevent attackers from moving laterally across the network and targeting high-value assets such as domain controllers.
Teams Security Warnings
Microsoft has also emphasized the importance of Teams security warnings, which explicitly flag communications from persons outside the organization and potential phishing attempts. These warnings can help users identify potential threats and take action to prevent them.
Conclusion
Microsoft Teams has become a prime target for threat actors seeking to exploit vulnerabilities in the platform for malicious purposes. The abuse of external Microsoft Teams collaboration by hackers to impersonate IT or helpdesk staff is a growing threat that businesses must be aware of. By following Microsoft’s recommendations and being cautious when interacting with external contacts, businesses can reduce the risk of falling victim to these types of attacks.
Practical Actionable Solutions
Here are some practical, actionable solutions that businesses can implement to prevent these types of attacks:
- Treat external Teams contacts as untrusted by default.
- Restrict or closely monitor remote assistance tools, such as Quick Assist.
- Limit WinRM usage to controlled systems.
- Implement robust security measures, such as multi-factor authentication and regular software updates.
- Monitor network traffic and system activity for suspicious behavior.
- Conduct regular security audits and penetration testing to identify vulnerabilities.
- Train employees on security best practices and phishing detection.
By implementing these solutions, businesses can reduce the risk of falling victim to these types of attacks and protect their sensitive data from being exfiltrated.
Final Thoughts
As Microsoft Teams continues to grow in popularity, it is essential for businesses to be aware of the threats associated with its use. By following Microsoft’s recommendations and implementing robust security measures, businesses can reduce the risk of falling victim to these types of attacks and protect their sensitive data from being exfiltrated.
The abuse of external Microsoft Teams collaboration by hackers to impersonate IT or helpdesk staff is a growing threat that businesses must be aware of. By being cautious when interacting with external contacts and implementing robust security measures, businesses can reduce the risk of falling victim to these types of attacks and protect their sensitive data from being exfiltrated.
