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 <[email protected]>
BETAVERSiON Systems [www.betaversion.net]
info/pgp: finger [email protected]
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