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                     Symantec Vulnerability Research
                     http://www.symantec.com/research
                           Security Advisory

   Advisory ID: SYMSA-2007-010
Advisory Title: Microsoft ActiveSync 4.x Weak Password Obfuscation
        Author: Ollie Whitehouse / ollie_whitehouse@symantec.com
  Release Date: 15-10-2006
   Application: ActiveSync 4.x
      Platform: Microsoft Windows
      Severity: Information Disclosure
 Vendor status: Update available
    CVE Number: CVE-2007-5460
     Reference: http://www.securityfocus.com/bid/25976


Overview:

Microsoft ActiveSync 4.1 acts as the gateway between your Windows
powered PC and Windows Mobile powered device, enabling the transfer
of Outlook information, Office documents, pictures, music, videos and
applications from your desktop to your device.

A vulnerability has been discovered in the mechanism that Microsoft
uses to obfuscate the password when it's sent over the USB network
interface between the device and the host machine. This enables malicious
software on the host to either impersonate a device in order to obtain
the current password or, if in a position to sniff network traffic, obtain
the password for trivial decoding.


Details:

When a device is docked via USB it uses the connection like a standard
network interface. Once an IP address is obtained the device will
initially communicate via RAPI with the host on port 990/TCP. It will
go through a small handshake routine and then, if appropriate, challenge
the host for the devices PIN or Password. When the user supplies this
PIN/Password on the host it will be obfuscated via XOR with a fixed key
of E9 and then sent over the USB network connection to the device for
verification.

This process results in two vulnerabilities. Firstly, should an attacker
be in a position to sniff the host computer's network connection he will
be able to recover the PIN/Password. Secondly, an attacker can spoof the
docking process of the device in an attempt to get the user to supply
his PIN/Password.

If we take a sample packet:

0000  82 00 60 0f e8 00 80 00  60 0f e8 00 08 00 45 00   ..`..... `.....E.
0010  00 32 59 95 40 00 80 06  49 31 a9 fe 02 02 a9 fe   .2Y.@... I1......
0020  02 01 03 de 05 d0 e8 c0  cb c0 56 2e 41 75 50 18   ........ ..V.AuP.
0030  fa 6a 91 dd 00 00 08 00  d8 e9 db e9 da e9 dd e9   .j...... ........

We can see that byte 36 is the length of the password (8 bytes) followed by
a NULL. After which is the password obfuscated with E9, this is immediately
apparent due to the use of a UNICODE string for the password so every second
byte is 0x00 XOR 0xE9 which equals 0xE9.

Vendor Response:

There is a security vulnerability that could allow for Information Disclosure.
An attacker would need to do one of two things, either tether a cable to the
USB sync cable or bind a network sniffer to the USB-RNDIS interface - requiring
administrative permissions on the workstation hosting the AS connection.

Recommendation:

Windows Mobile 5.0 Please see your handset manufacturer to obtain the update
customized for your device. This issue is fixed in Windows Mobile 6.


Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned
the following names to these issues.  These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.


CVE-2007-5460  Requested

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