Software Engineering Institute

Outlook Web Access (OWA) is a component of Microsoft Exchange. By using OWA, a server that is running Exchange Server can also function as a website that lets authorized users read or send email messages, manage their calendar, or perform other mail functions over the Internet by using a web browser. A cross-site scripting vulnerability exists in the way OWA validates user input provided to an HTML redirection query.

By convincing a user to click on a specially crafted URL within an email message, an attacker could cause arbitrary scripting code to be executed in the victim's browser. If executed, the script would have all privileges of the OWA user, including access to and manipulation of messages and folders on the server.

If an attacker can convince a user to follow a link, the attacker could execute script as the victim in the context of the zone in which the Outlook Web Access server resides. For example, this could permit the attacker to gain access to messages stored on the server.
According to the Microsoft Security Bulletin:
It may also be possible to exploit the vulnerability to manipulate Web browser caches and intermediate proxy server caches and put spoofed content in those caches.

Apply patch

Apply a patch as described in Microsoft Security Bulletin MS04-026.

Disable Outlook Web Access

Until a patch can be applied, you may wish to disable Outlook Web Access for each affected Exchange site. You can do this by performing the following steps:

1. Start Exchange Administrator.
2. Expand the Configuration container for the site.
3. Click the Protocols container for the site.
4. Open the properties of the HTTP (Web) Site Settings object.
5. Click to clear the Enable Protocol check box.
6. Wait for the change to replicate, and then verify that this change has replicated to each server in the site. To do this, bind to each server in the site with Exchange Administrator, and then view the setting.