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             AUSCERT External Security Bulletin Redistribution

                              ESB-2009.1235.3
        Vulnerability in Internet Information Services FTP Service
                   Could Allow for Remote Code Execution
                             7 September 2009

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Microsoft Internet Information Server 5.0
                   Microsoft Internet Information Server 5.1
                   Microsoft Internet Information Server 6.0
                   Microsoft Internet Information Server 7.0
Publisher:         Microsoft
Operating System:  Windows
Impact/Access:     Execute Arbitrary Code/Commands -- Remote/Unauthenticated
                   Denial of Service               -- Remote/Unauthenticated
Resolution:        Mitigation
CVE Names:         CVE-2009-3023 CVE-2009-2521 

Original Bulletin: 
   http://www.microsoft.com/technet/security/advisory/975191.mspx

Comment: Microsoft has updated this advisory to include a Denial of Service
         and further information.

Revision History:  September 7 2009: Updated with information regarding DoS
                                     and relevant CVE
                   September 2 2009: Updated to the Microsoft Security Advisory
                   September 1 2009: Initial Release

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Microsoft Security Advisory (975191)

Vulnerabilities in the FTP Service in Internet Information Services

Published: September 01, 2009 | Updated: September 03, 2009

Version: 2.0

General Information

Executive Summary

  Microsoft is investigating new public reports of vulnerabilities in the FTP
  Service in Microsoft Internet Information Services (IIS) 5.0, Microsoft
  Internet Information Services (IIS) 5.1, Microsoft Internet Information
  Services (IIS) 6.0, and Microsoft Internet Information Services (IIS) 7.0.
  The vulnerabilities could allow remote code execution (RCE) on systems
  running FTP Service on IIS 5.0, or denial of service (DoS) on systems
  running FTP Service on IIS 5.0, IIS 5.1, IIS 6.0 or IIS 7.0.

  Microsoft is aware that detailed exploit code has been published on the
  Internet for these vulnerabilities. Microsoft is currently aware of limited
  attacks that use this exploit code. Microsoft is actively monitoring this
  situation to keep customers informed and to provide customer guidance as
  necessary.

  We are actively working with partners in our Microsoft Active Protections
  Program (MAPP) to provide information that they can use to provide broader
  protections to customers.

  Upon completion of this investigation, Microsoft will take the appropriate
  action to help protect our customers. This may include providing a security
  update through our monthly release process or providing an out-of-cycle
  security update, depending on customer needs.

  These vulnerabilities were not responsibly disclosed to Microsoft and may put
  computer users at risk. We continue to encourage responsible disclosure of
  vulnerabilities. We believe the commonly accepted practice of reporting 
  vulnerabilities directly to a vendor serves everyone's best interests. This
  practice helps to ensure that customers receive comprehensive, high-quality
  updates for security vulnerabilities without exposure to malicious attackers
  while the update is being developed.

CVE Reference
	
  CVE-2009-3023 (RCE on IIS 5.0 and DoS on IIS 5.1 and IIS 6.0)
  CVE-2009-2521 (DoS on IIS 5.0, IIS 5.1, IIS 6.0, and IIS 7.0)

Affected  Software

Operating System                          Component

Microsoft Windows 2000                    Microsoft Internet Information 
Service Pack 4                            Services 5.0 (FTP Service 5.0) 

Windows XP Service Pack 2 and             Microsoft Internet Information
Windows XP Service Pack 3                 Services 5.1 (FTP Service 5.1)

Windows XP Professional x64 Edition       Microsoft Internet Information
Service Pack 2                            Services 6.0 (FTP Service 6.0)

Windows Server 2003                       Microsoft Internet Information
Service Pack 2                            Services 6.0 (FTP Service 6.0)
	
Windows Server 2003 x64 Edition           Microsoft Internet Information
Service Pack 2                            Services 6.0 (FTP Service 6.0)
	
Windows Server 2003 with SP2              Microsoft Internet Information
for Itanium-based Systems                 Services 6.0 (FTP Service 6.0)
	
Windows Vista, Windows Vista              Microsoft Internet Information
Service Pack 1, and Windows Vista         Services 7.0 (FTP Service 6.0)
Service Pack 2

Windows Vista x64 Edition,                Microsoft Internet Information
Windows Vista x64 Edition                 Services 7.0 (FTP Service 6.0)
Service Pack 1, and Windows Vista x64
Edition Service Pack 2
	
Windows Server 2008 for 32-bit Systems    Microsoft Internet Information
and Windows Server 2008 for 32-bit        Services 7.0 (FTP Service 6.0)
Systems Service Pack 2
	
Windows Server 2008 for x64-based         Microsoft Internet Information
Systems and Windows Server 2008 for       Services 7.0 (FTP Service 6.0)
x64-based Systems Service Pack 2
	
Windows Server 2008 for Itanium-based     Microsoft Internet Information
Systems and Windows Server 2008 for       Services 7.0 (FTP Service 6.0)
Itanium-based Systems Service Pack 2
	
Mitigating Factors

Mitigation refers to a setting, common configuration, or general best-practice,
existing in a default state, that could reduce the severity of this issue. The
following mitigating factors may be helpful in your situation:

  * FTP Service is not installed by default on all supported editions of
    Microsoft Windows 2000, Windows XP, and Windows Server 2003.

  * Internet Information Services 5.1 on Window XP and Internet Information
    Services 6.0 on Windows Server 2003 are at reduced risk because these
    versions were compiled using the /GS compiler option. This does not remove
    the vulnerability but does make exploitation of the vulnerability more
    difficult and reduces the impact to a denial of service.

Workarounds

Workaround refers to a setting or configuration change that does not correct the
underlying issue but would help block known attack vectors before you apply the
update. Microsoft has tested the following workarounds and states in the
discussion whether a workaround reduces functionality:
	
  * Do not allow FTP write access to anonymous users

    This workaround blocks remote code execution attacks from anonymous users.
    With this workaround, all affected versions of IIS are still vulnerable to
    denial of service attacks from anonymous users.

    This workaround blocks known exploits and minimizes the impact of any
    variations of this attack vector. However, this workaround does not render
    the vulnerability completely inaccessible to exploitation.

    Anonymous users are not granted FTP write access by default. If anonymous
    write access has been granted on an FTP server, the administrator can
    modify IIS permissions to prevent anonymous write access. Anonymous users will
    not be able to cause a remote code execution with this workaround.

    To modify IIS permissions to prevent FTP write access to anonymous users,
    perform the following steps:

    1. Launch IIS Manager.

    2. Right click Default FTP Site and point to Properties.

    3. Click the Home Directory tab.

    4. Ensure that Write is deselected.

    Impact of Workaround: Anonymous users will not have the ability to publish
    content on the server using the FTP Service.
	
    * Do not allow FTP access to anonymous users

    This workaround blocks denial of service attacks from unauthenticated users
    without a valid user account.

    This workaround blocks known exploits and minimizes the impact of any
    variations of this attack vector. However, this workaround does not render
    the vulnerability completely inaccessible to exploitation.

    Anonymous users are not granted FTP write access by default. If anonymous write
    access has been granted on an FTP server, the administrator can modify IIS
    permissions to prevent anonymous write access. Anonymous users will not be able
    to exploit the vulnerability with this workaround.

    To modify IIS permissions to prevent FTP write access to anonymous users,
    perform the following steps:

    1. Launch IIS Manager.

    2. Right click Default FTP Site and point to Properties.

    3. Click the SecurityAccounts tab.

    4. Ensure that Allow anonymous connections is deselected.

    Impact of Workaround: Anonymous users will not have access to the FTP Service.
	
    * Modify NTFS file system permissions to disallow directory creation by FTP users

    This workaround blocks remote code execution attacks from authenticated users.
    With this workaround, all affected versions of IIS server are still vulnerable
    to denial of service attacks from authenticated users.

    This workaround blocks known exploits and minimizes the impact of any
    variations of this attack vector. However, this workaround does not render
    the vulnerability completely inaccessible to exploitation.

    An administrator can modify NTFS file system permissions on the root directories
    of FTP sites hosted on a server to disallow creation of directories by FTP users.
    This modification still allows FTP users to upload files to existing directories.
    Authenticated and unauthenticated users will not be able to cause a remote code
    execution with this workaround.

    As administrator, perform the following steps to remove directory creation
    privileges from the Users group. If you have a configured FTP user or custom
    group to manage your FTP users, replace the Users group in Step 5 below with
    these custom identities.

    1. Browse to the root directory of your FTP site. By default this is in
       %systemroot%\inetpub\ftproot.

    2. Right-click the directory and select Properties.

    3. Click the Security tab and click Advanced.

    4. Click Change Permissions.

    5. Select the Users group and click Edit.

    6. Deselect Create Folders/Append Data.

    Impact of Workaround: FTP users will not be able to create directories
    through the FTP Service. FTP users will still be able to upload files to
    existing directories through the FTP Service.
	
    * Upgrade to FTP Service 7.5

    FTP Service 7.5 is available for Windows Vista and Windows Server 2008. This
    version of FTP Service is not affected by the vulnerabilities in this advisory.
    See the following sites on Download Center:
	
    - Microsoft FTP Service 7.5 for IIS 7.0 (x86) [1]
    - Microsoft FTP Service 7.5 for IIS 7.0 (x64) [2]

    Impact of Workaround: FTP sites will need to be migrated from FTP Service 6.0
    to FTP Service 7.5.
	
    * Disable the FTP Service

    This workaround will completely block the known attack vector or any
    variations thereof. See Microsoft Knowledge Base Article 321141, "How To
    Disable or Remove Unnecessary IIS Services."

    Impact of Workaround: FTP Service will be disabled.

    [1] Microsoft FTP Service 7.5 for IIS 7.0 (x86)
        http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=b7f5b652-8c5c-447a-88b8-8cfc5c13f571

    [2] Microsoft FTP Service 7.5 for IIS 7.0 (x64)
        http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=ffb7c167-279e-48d3-8169-dea85784c4d1

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