Microsoft Exchange Server CVE-2017-8758 Cross Site Scripting Vulnerability

Description

Microsoft Exchange Server is prone to a cross-site scripting vulnerability because it fails to 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 can allow the attacker to steal cookie-based authentication credentials and to launch other attacks. Microsoft Exchange Server 2016 Cumulative Update 6 is vulnerable.

Technologies Affected

• Microsoft Exchange Server 2016 Cumulative Update 6

Recommendations

Block external access at the network boundary, unless external parties require service.
If global access isn’t needed, filter access to the affected computer at the network boundary. Restricting access to only trusted computers and networks might greatly reduce the likelihood of a successful exploit.

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.

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 JavaScript.
Since exploiting cross-site scripting issues often requires the execution of malicious script code in web clients, 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 websites that rely on the execution of browser-based script code.

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