CVE-2020-3535 in Webex Teams Client
Summary
by MITRE • 10/08/2020
A vulnerability in the loading mechanism of specific DLLs in the Cisco Webex Teams client for Windows could allow an authenticated, local attacker to load a malicious library. To exploit this vulnerability, the attacker needs valid credentials on the Windows system. The vulnerability is due to incorrect handling of directory paths at run time. An attacker could exploit this vulnerability by placing a malicious DLL file in a specific location on the targeted system. This file will execute when the vulnerable application launches. A successful exploit could allow the attacker to execute arbitrary code on the targeted system with the privileges of another user’s account.
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Analysis
by VulDB Data Team • 11/17/2020
The vulnerability identified as CVE-2020-3535 resides within the Cisco Webex Teams client for Windows operating system, specifically targeting the dynamic link library loading mechanism. This flaw represents a critical security weakness that could be exploited by authenticated local attackers who possess valid system credentials. The vulnerability stems from improper handling of directory paths during runtime execution, creating an exploitable condition where malicious code can be loaded and executed without user interaction. The affected application fails to properly validate or sanitize the paths used for DLL resolution, allowing an attacker to manipulate the loading sequence through strategic placement of malicious files within the system's file structure.
The technical implementation of this vulnerability follows a classic dynamic link library hijacking pattern where the application's runtime environment searches for required libraries in a predictable order. When the Webex Teams client launches, it attempts to load specific DLL dependencies from predetermined locations, including the current working directory and system paths. An attacker who has gained local access to a Windows system can place a malicious DLL with the same name as a legitimate dependency in a location that will be searched before the genuine library. This behavior aligns with CWE-426 Untrusted Search Path vulnerability classification, which occurs when applications search for libraries in directories that can be manipulated by unprivileged users. The vulnerability operates under the principle that applications trust the path resolution process without sufficient validation of the library's authenticity or source.
The operational impact of this vulnerability extends beyond simple code execution, as it enables privilege escalation scenarios within the Windows environment. When a malicious DLL is successfully loaded and executed, the code runs with the privileges of the user account that launched the vulnerable application, potentially allowing attackers to access sensitive data, modify system configurations, or establish persistent access points. This exploitation vector represents a significant threat in enterprise environments where users may have elevated privileges or access to sensitive corporate resources through their Webex Teams sessions. The vulnerability's local nature means that attackers must first gain a foothold on the system through other means, but once established, they can leverage this weakness to escalate their access level and maintain persistent presence within the targeted environment.
Security professionals should implement multiple layers of mitigation to address this vulnerability effectively. The primary defense mechanism involves ensuring that all system paths are properly secured and that applications perform strict validation of library locations before loading dependencies. This includes implementing proper access controls on directories where application libraries are stored, as well as configuring applications to use absolute paths for library loading rather than relying on relative or environment-based path resolution. System administrators should also consider implementing application whitelisting policies and monitoring for suspicious DLL loading activities. According to ATT&CK framework, this vulnerability maps to T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation, indicating that exploitation efforts would likely involve code injection techniques and privilege escalation methods. Organizations should also ensure that Cisco Webex Teams clients are regularly updated to versions that address this specific vulnerability, as the manufacturer has released patches to correct the directory path handling behavior and prevent unauthorized library loading.