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Microsoft Teams Security Bypass: A Deep Dive

Publication Date: 2025/11/28 14:48:03

Attackers Can Bypass Any and All Teams Security Measures

Microsoft Teams’ security features,while robust,are not impenetrable. Researchers have demonstrated that attackers can bypass thes measures using a relatively simple technique involving malicious links and the platform’s built-in app integration capabilities. This vulnerability allows attackers to deliver malware and potentially gain control of user accounts.

How the bypass Works

The core of the bypass lies in how Teams handles links within custom applications. Attackers create a malicious app that, when installed, intercepts links clicked within Teams. Instead of opening the intended URL, the link is redirected through a server controlled by the attacker. This allows them to:

• Deliver malware disguised as legitimate content.
• Steal user credentials through phishing attacks.
• Gain unauthorized access to sensitive data.

The Role of Custom Apps

Teams’ extensibility through custom apps is a key feature, but it also introduces a potential attack vector.The app manifest, which defines the app’s behavior, can be crafted to exploit the link handling mechanism. Specifically, the outgoingWebhook functionality is ofen misused.

Understanding the Technical Details

The attack leverages the outgoingWebhook feature, which allows apps to receive notifications when messages are posted in Teams channels. Attackers register a malicious webhook that intercepts links. When a user clicks a link, the app redirects it through the attacker’s server before sending it to the intended destination. This redirection is often invisible to the user.

The Impact of Redirection

This redirection allows attackers to perform several malicious actions:

• Malware Delivery: the attacker can serve malware from their server instead of the legitimate website.
• Phishing: The attacker can redirect the user to a fake login page designed to steal their credentials.
• Data Exfiltration: The attacker can intercept sensitive data transmitted through the link.

Mitigation Strategies

Organizations can take several steps to mitigate this risk:

• Strict App Governance: Implement a rigorous app approval process. Only allow trusted apps to be installed in your Teams habitat.
• Regular Security Audits: Conduct regular security audits of your Teams configuration and installed apps.
• User Awareness Training: Educate users about the risks of clicking on suspicious links, even within Teams.
• Conditional Access Policies: Implement conditional access policies to restrict access to sensitive resources based on user identity and device posture.
• Monitor Outgoing Webhooks: Regularly monitor and review all configured outgoing webhooks for suspicious activity.

Key Takeaways

• Teams security is not foolproof and can be bypassed through malicious apps.
• The outgoingWebhook feature is a common attack vector.
• strong app governance and user awareness are crucial for mitigating the risk.

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