CVE-2020-10146 in Teams
Summary
by MITRE • 12/09/2020
The Microsoft Teams online service contains a stored cross-site scripting vulnerability in the displayName parameter that can be exploited on Teams clients to obtain sensitive information such as authentication tokens and to possibly execute arbitrary commands. This vulnerability was fixed for all Teams users in the online service on or around October 2020.
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Analysis
by VulDB Data Team • 12/13/2020
The vulnerability identified as CVE-2020-10146 represents a critical stored cross-site scripting flaw within Microsoft Teams online service that specifically targets the displayName parameter. This weakness resides in the web application layer of the Teams platform and demonstrates how seemingly benign user input fields can become entry points for sophisticated attacks. The vulnerability affects the Microsoft Teams client applications and represents a significant security risk due to the privileged nature of the information that can be accessed through exploitation. The flaw was particularly concerning as it impacted all Teams users and required immediate remediation across the entire Microsoft Teams ecosystem.
The technical implementation of this vulnerability stems from inadequate input validation and output encoding within the Teams service architecture. When users provide data through the displayName parameter, the system fails to properly sanitize or escape special characters that could be interpreted as executable code by web browsers. This stored XSS vulnerability allows attackers to inject malicious scripts that persist in the application's database and execute whenever other users view the affected content. The attack vector specifically leverages the Teams client's handling of user profile information, where the displayName field serves as an accessible input point that bypasses normal security controls. This flaw aligns with CWE-79 which categorizes cross-site scripting vulnerabilities as weaknesses in input validation and output encoding mechanisms.
The operational impact of CVE-2020-10146 extends beyond simple data theft to encompass potential full system compromise through token hijacking and command execution capabilities. Attackers who successfully exploit this vulnerability can obtain authentication tokens that grant them elevated privileges within the Teams environment, potentially allowing access to sensitive communications, user data, and collaboration resources. The ability to execute arbitrary commands through this vector creates a pathway for attackers to establish persistent access, escalate privileges, and move laterally within the Microsoft 365 ecosystem. This vulnerability directly maps to several ATT&CK techniques including T1078 for valid accounts and T1566 for social engineering, as attackers could leverage compromised tokens to gain unauthorized access to additional services.
Microsoft addressed this vulnerability through a comprehensive patch deployment that updated all Teams online service instances and client applications. The remediation process involved implementing stricter input validation controls, enhancing output encoding mechanisms, and strengthening the sanitization of user-provided content. Security teams should verify that all Teams clients are updated to the latest versions and that proper input validation is implemented at all application layers. Organizations using Microsoft Teams should conduct regular security assessments to ensure that similar vulnerabilities do not exist in custom integrations or third-party applications that connect to the Teams platform. The incident highlights the importance of continuous security monitoring and the need for robust input validation across all web applications to prevent similar stored XSS vulnerabilities from compromising user data and system integrity.