Title: OWA Function Allows Unauthenticated User to Enumerate
Global Address List
Date: 06 September 2001
Software: Exchange 5.5
Impact: Information Disclosure
Bulletin: MS01-047

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-047.asp.

Issue:

Among the functions Outlook Web Access (OWA) in Exchange 5.5 offers
is the ability to search the global address list (GAL). By design,
this is an authenticated function, implemented as a two-tier
architecture - a front tier that provides a user interface and a
back-end tier that actually performs the search. However, only the
front tier actually checks authentication. An attacker who sent a
properly formatted request to the back-end function that actually
performs the search could enumerate the GAL without authenticating.

Mitigating Factors:

• The vulnerability would only allow the attacker to learn
  users' email aliases. It would not provide any other
  capabilities. Specifically, it would not give the attacker
  any way to create or send mail as a user; to read, change
  or delete mail; or to perform any other functions on the
  server.
• The vulnerability is only exploitable via OWA. Exchange
  servers that are not configured to offer OWA are not affected
  by the vulnerability.
• The vulnerability does not affect Exchange 2000, even when
  offering OWA.

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms01-047.asp
  for information on obtaining this patch.

Acknowledgment:

• Noam Rathaus from SecuriTeam.com (http://www.SecuriTeam.com)

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