Title: Incorrect Attachment Handling in Exchange 2000 OWA
Can Execute Script
Date: 06 June 2001
Software: Microsoft Exchange 2000 Server Outlook Web Access
Impact: Run code of attacker's choice
Bulletin: MS01-030

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-030.asp.

Issue:

OWA is a service of Exchange 2000 Server that allows users to use a
web
browser to access their Exchange mailbox. However, a flaw exists in
the
interaction between OWA and IE for message attachments. If an
attachment contains HTML code including script, the script will be
executed when the attachment is opened, regardless of the attachment
type. Because OWA requires that scripting be enabled in the zone
where
the OWA server is located, this script could take action against the
user's Exchange mailbox.

An attacker could use this flaw to construct an attachment containing
malicious script code. The attacker could then send the attachment in
a
message to the user. If the user opened the attachment in OWA, the
script would execute and could take action against the user's mailbox
as if it were the user, including, under certain circumstances,
manipulation of messages or folders.

Mitigating Factors:

• The vulnerability could only be exploited if the user were
  using OWA in conjunction with IE.
• The vulnerability is only exploitable by attachments that
  are received via OWA. In general, an attacker would have
  no way to determine whether a user would open an
  attachment using OWA rather than an Outlook client.
• An attacker's ability to exploit this vulnerability would
  require that she entice the user to open an attachment
  from an untrusted source. Best practices recommend against
  opening any attachment from an unknown or untrusted source.

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin
  http://www.microsoft.com/technet/security/bulletin/ms01-030.asp
  for information on obtaining this patch.

Acknowledgment:

• Joao Gouveia ([email protected])

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