raidsonic nas-4220 crypt disk key leak (stored in plain on unencrypted partition)

Manufacturer: RaidSonic (www.raidsonic.de)
Device: NAS-4220-B
Firmware: 2.6.0-n(2007-10-11)
Device Type: end user grade NAS box
OS: Linux 2.6.15
Architecture: ARM
Designed by: Storm Semiconductor Inc (www.storlinksemi.com)

Problem:
 Hard disk encryption key stored in plain on unencrypted partition.

Time line:
 Found: 09. March 2008
 Reported: 09. March 2008
 Disclosed: 16. March 2008

Summary:
 The NAS-4220-B offers disk encryption through it's web interface. The
 key used for encrypting the disk(s) is stored on a unencrypted
 partition. Therefore one can extract the encryption key by removing
 the disk from the NAS and reading the value from the unencrypted
 partition. The key itself is stored in a file in plain (base64
 encoded). Therefore the NAS-4220 crypt disk support can not be
 considered secure.

Details:
 The NAS-4220-B can hold two SATA disks. Disk are encrypted through a
 loop back device using AES128. The problem came to my attention when
 I could access the NAS after reboot without suppling the hard disk key.
 
 The key is stored in /system/.crypt, "/system" is a small
 configuration partition on the same disk that holds the encrypted
 partition. The system partition is created by the system software
 running on the NAS-4220. The configuration partition of the second
 hard disk is not mounted by default but also contains the .crypt file
 holding the key for the encrypted partition on the same disk.

 Accessing the key (key value is the example I used):
  $ cat /system/.crypt
  MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=
 
  key in plain key in base64
  12345678901234567890 MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=

 Base64 decode:
  #!/usr/bin/python
  from base64 import *
  print b64decode("MTIzNDU2Nzg5MDEyMzQ1Njc4OTA=")

Reported by:
 Collin Mulliner <collin(AT)betaversion.net >

Collin's Advisories: http://www.mulliner.org/security/advisories/

--
Collin R. Mulliner <collin_at_betaversion.net>
BETAVERSiON Systems [www.betaversion.net]
info/pgp: finger collin_at_betaversion.net
If you have to run heating in winter, you don't own enough computers.