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Microsoft ActiveSync 4.x Weak Password Obfuscation
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SUMMARY
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.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-5460>
CVE-2007-5460
ADDITIONAL INFORMATION
The information has been provided by
<mailto:ollie_whitehouse@symantec.com> Ollie Whitehouse.
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