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Windows FTP Client Allows File Transfer Location Tampering (MS05-044)
------------------------------------------------------------------------
SUMMARY
A tampering vulnerability exists in the Windows FTP client. This
vulnerability could allow an attacker to modify the intended destination
location for a file transfer, when a client has manually chosen to
transfer a file by using FTP. This vulnerability could allow the attacker
to write the file to any file system that is located on an affected
system.
DETAILS
Affected Software:
* Microsoft Windows XP Service Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=351C63A3-AB62-418D-8678-3AF791D73A29>
Download the update
* Microsoft Windows Server 2003 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=4940CF64-E1FD-4E88-8980-3106BE03BF12>
Download the update
* Microsoft Windows Server 2003 for Itanium-based Systems -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=B715147B-DE2D-4F14-9548-AFF18641D0F3>
Download the update
Affected Components:
* Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service
Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=FCEA60E5-9EA8-4216-BA4D-C85054892DBB>
Download the update
Non-Affected Software:
* Microsoft Windows 2000 Service Pack 4
* Microsoft Windows XP Service Pack 2
* Microsoft Windows XP Professional x64 Edition
* Microsoft Windows Server 2003 Service Pack 1
* Microsoft Windows Server 2003 with SP1 for Itanium-based Systems
* Microsoft Windows Server 2003 x64 Edition
* Microsoft Windows 98, Microsoft Windows 98 Second Edition (SE), and
Microsoft Windows Millennium Edition (ME)
Non-Affected Components:
* Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service
Pack 4
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2126>
CAN-2005-2126
Mitigating Factors for FTP Client Vulnerability:
* If an attacker successfully persuades users to visit an FTP server
hosting files with specially-crafted file names, the attacker would have
no way of forcing files to be transferred. User interaction is required
before the file can be transferred to the affected system.
* If the malicious FTP transfer tries to overwrite an existing file on
the affected system, the user receives an Overwrite File warning
message. The file is saved only if the user selects to allow it to save
when they receive the warning message.
* By default, the Enable Folder View for FTP Sites Internet Explorer
setting is disabled on all affected operating system versions. An attacker
would only be successful if the user manually enables the Enable Folder
View for FTP Sites Internet Explorer setting on the affected system.
What is the scope of the vulnerability?
This is a tampering vulnerability. This vulnerability could allow an
attacker to modify the intended destination location for a file transfer
when a client has manually chosen to transfer a file by using FTP.
What causes the vulnerability?
The Windows FTP client does not properly validate file names that are
received from FTP servers.
What might an attacker use the vulnerability to do?
An attacker who exploited this vulnerability could save files to specific
locations on an affected system. These files could allow other attacks.
For example, an attacker could save an executable file in the Startup
folder. Then, the transferred file would run the next time the user logs
on.
Who could exploit the vulnerability?
Anyone who could persuade a user to visit and transfer files from an FTP
server that hosts files that have specially-crafted file names.
How could an attacker exploit the vulnerability?
An attacker could exploit this vulnerability by hosting a file on an FTP
server that has a specially-crafted file name. The file name must be
constructed in such a way that it bypasses the file name validation that
the FTP client provides and that it maps to a valid location on the users
computer. An attacker must then persuade a user to download this file.
Can the vulnerability be exploited automatically by visiting an FTP
server?
No. User interaction is required for the file to be transferred and saved
by using FTP.
What systems are primarily at risk from the vulnerability?
The vulnerability requires that a user connect to an FTP server and
transfer files from the FTP server. Therefore, any systems where FTP
transfers occur frequently, such as workstations, are at the most risk
from this vulnerability. Systems that are not typically used to visit FTP
servers, such as most server systems, are at a reduced risk.
What does the update do?
The update removes the vulnerability by modifying the way the Windows FTP
client validates file names that it receives from FTP servers.
When this security bulletin was issued, had this vulnerability been
publicly disclosed?
Yes. This vulnerability has been publicly disclosed. It has been assigned
Common Vulnerability and Exposure number CAN-2005-2126
When this security bulletin was issued, had Microsoft received any reports
that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this
vulnerability had been publicly used to attack customers. However,
examples of proof of concept code had been published when this security
bulletin was originally issued.
Does applying this security update help protect customers from the code
that has been published publicly that tries to exploit this vulnerability?
Yes. This security update addresses the vulnerability for which proof of
concept code has been published.
ADDITIONAL INFORMATION
The information has been provided by Microsoft Product Security.
The original article can be found at:
<http://www.microsoft.com/technet/security/Bulletin/MS05-044.mspx>
http://www.microsoft.com/technet/security/Bulletin/MS05-044.mspx
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