Microsoft Outlook Web Access is prone to a script-injection vulnerability because the application fails to properly handle specially crafted email attachments. To exploit this issue, attackers must send specially crafted files through email messages to users of the affected application. When users open the file, attacker-supplied script code will be executed in the context of the affected website. Successful exploits allow attackers to access Outlook Web Access sessions with the privileges of the targeted user. As a result, attackers may be able to obtain sensitive information and send, modify, or delete email; other attacks are also possible.
Run all software as a nonprivileged user with minimal access rights.
Attackers may successfully exploit client flaws in the browser through script-injection 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 accept or execute files from untrusted or unknown sources.
Do not open email or email attachments that originate from unknown or untrusted sources.
Set web browser security to disable the execution of script code or active content.
Since a successful exploit of this issue allows malicious code to execute in web clients, consider disabling support for script code and active content within the client browser. Note that this mitigation tactic might adversely affect legitimate websites that rely on the execution of browser-based script code.
The vendor has released an advisory along with updates to address this issue. Please see the referenced advisory for more information.