Title: Function Exposed via LDAP over SSL Could Enable
Passwords to be Changed
Date: 25 June 2001
Software: Windows 2000
Impact: Privilege Elevation
Bulletin: MS01-036

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-036.asp.

Issue:

This vulnerability involves an LDAP function that is only available
if
the LDAP server has been configured to support LDAP over SSL
sessions,
and whose purpose is to allow users to change the data attributes of
directory principals. By design, the function should check the
authorizations of the user before completing the request; however, it
contains an error that manifests itself only when the directory
principal is a domain user and the data attribute is the domain
password – when this is the case, the function fails to check the
permissions of the requester, with the result that it could be
possible
for a user to change any other user's domain login password.

An attacker could change another user's password for either of two
purposes: to cause a denial of service by preventing the other user
from logging on, or in order to log into the user's account and gain
any privileges the user had. Clearly, the most serious case would be
one in which the attacker changed a domain administrator's password
and
logged into the administrator's account.

By design, the function affected can be called by any user who can
connect to the LDAP server, including users who connect via anonymous
sessions. As a result, any user who could establish a connection with
an affected server could exploit the vulnerability.

Mitigating Factors:

• LDAP over SSL sessions cannot be conducted unless the
  administrator has installed a digital certificate on the LDAP
  server. As a result, default installations of Windows 2000
  are not affected by this vulnerability.
• If the firewall is configured to block tcp port 636, the
  vulnerability could not be exploited by outside users.
• This vulnerability could not be used to change the password
  of local user accounts on individual machines.

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin
  http://www.microsoft.com/technet/security/bulletin/ms01-036.asp
  for information on obtaining this patch.

Acknowledgment:

• Jon McDonald (http://www.entrigue.net)
• Russ Cooper (http://www.ntbugtraq.com)

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