Microsoft Skype for Business and Lync Server CVE-2015-2531 Cross Site Scripting Vulnerability

Description

Microsoft Skype for Business and Microsoft Skype Lync Server are prone to a cross-site scripting vulnerability because they fail to sufficiently sanitize user-supplied input. An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may allow the attacker to steal cookie-based authentication credentials and launch other attacks.

Technologies Affected

• Microsoft Lync Server 2013
• Microsoft Skype for Business Server 2015

Recommendations

Run all software as a nonprivileged user with minimal access rights.
Attackers may successfully exploit client flaws in the browser through cross-site scripting vulnerabilities. When possible, run client software as regular user accounts with limited access to system resources. This may limit the immediate consequences of client-side vulnerabilities.

Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to detect and block attacks and anomalous activity such as requests containing suspicious URI sequences. Since the webserver may log such requests, review its logs regularly.

Do not follow links provided by unknown or untrusted sources.
Web users should be cautious about following links to websites that are provided by unfamiliar or suspicious sources. Filtering HTML from emails may help remove a possible vector for transmitting malicious links to users.

Set web browser security to disable the execution of script code or active content.
Since exploiting cross-site scripting issues often requires malicious script code to run in browsers, consider disabling script code and active content support within a client browser as a way to prevent a successful exploit. Note that this mitigation tactic might adversely affect legitimate sites that rely on the execution of browser-based script code.

Updates are available. Please see the references or vendor advisory for more information.