Denial of Service Using Invalid Outlook Web Access Request New

A security vulnerability exists in Exchange 2000 Outlook Web Access which could allow a remote user to cause a denial of service attack by issuing a GET request for an invalid URL that contains a large number of invalid nested folders.

Issue

Because OWA will accept and process a request for an item in an authenticated user’s mailbox without verifying first that the folder structure is valid. An attacker could mount a denial of service attack by repeatedly levying a request for a non-existent but deeply nested folder in his own mailbox.

Exploiting the vulnerability wouldn’t necessarily affect the OWA server itself. The effect of the vulnerability would be to cause the process servicing the attacker’s mailbox to consume most or all of the CPU availability on the server it was running on. In may cases, this process would run on the OWA server, and thus the effects would be seen there. However, if the process servicing the attacker’s mailbox ran on a back-end server, the effect of exploiting the vulnerability would be seen there. In any event, the affected server would resume normal service once the request was handled.

Affected Products

• Microsoft Exchange 2000

Download

Patch: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=32431

Further Details

Source: Microsoft Corporation

Reference: Microsoft Corporation

Updated: September 26, 2001

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