Deception has found a new home in Microsoft Teams. Cybercriminals are now exploiting this widely-used collaboration platform to deliver malware, and they’re doing it right under our noses. The attack is terrifyingly simple—threat actors impersonate IT support staff or trusted clients, establishing contact through Teams’ default settings that allow external communication. And let’s be honest, most companies never bother changing those settings.
The technique, known as Browser Cache Smuggling, is disturbingly clever. It leverages HTML5 and JavaScript to disguise malicious code as harmless cached resources. Traditional security tools? Useless. The malware slips through firewalls and antivirus software like a ghost through walls. It’s using legitimate features, after all. Nothing to see here, folks!
Browser Cache Smuggling turns legitimate features into weapons, letting malware float past security like a phantom through your defenses.
When users engage with these fake support contacts, they’re unwittingly stepping into a trap. The attackers often combine Teams-based attacks with email bombing campaigns, creating confusion that makes victims more vulnerable. Once trust is established, they deploy tools like AnyDesk for remote access. Game over.
DarkGate malware is particularly fond of this distribution method. It uses AutoIt scripts for execution and creates persistent files and registry entries. The real kicker? Zero obfuscation in the code. It doesn’t need to hide when it’s invited in through the front door.
The attack unfolds in stages: initial contact, social engineering, remote access tool installation, malware deployment, and finally, establishing persistence. Attackers frequently employ steganography techniques to conceal malicious payloads within seemingly harmless images sent via Teams chat. These attacks are particularly effective because they exploit how browsers determine cacheability based on content-type headers from server responses. By that point, attackers can steal data, harvest credentials, capture keystrokes, and even download additional payloads.
The impact? Devastating. Unauthorized access, system compromise, network infiltration—the works.
Companies with Teams implementations are sitting ducks. The malware hides in plain sight, masquerading as legitimate processes while extracting sensitive information. It’s the perfect digital trojan horse. Organizations can significantly improve their defenses by implementing threat intelligence platforms that offer real-time monitoring and automated responses to such sophisticated threats.
Who knew that the friendly collaboration tool connecting your workplace could become its greatest vulnerability? Teams: bringing people together—including hackers and their targets.
