[NT] DriveCrypt Security Model Bypass and Incorrect BIOS API Usage



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DriveCrypt Security Model Bypass and Incorrect BIOS API Usage
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SUMMARY

<http://www.securstar.com/disk_encryption.php> DriveCrypt is an "Ideal to
encrypt USB-disks/sticks, secondary disks /partitions, CDs, DVDs,
containers etc. DriveCrypt also allows to hide data in music files and
create hidden containers/ partitions: By entering the correct password,
the disks open, if however you are forced to reveal a password, you could
reveal a pre-configured fake password and the disk will open showing
fake, prepared information". The password checking routine of DriveCrypt
fails to sanitize the BIOS keyboard buffer before and after reading
passwords.

DETAILS

Vulnerable Systems:
* Secu Star's DriveCrypt Plus Pack version 3.9

DriveCrypt's pre-boot authentication routines use the BIOS API to read
user input via the keyboard. The BIOS internally copies the keystrokes in
a RAM structure called the BIOS Keyboard buffer inside the BIOS Data Area.
This buffer is not flushed after use, resulting in potential plain text
password leakage once the OS is fully booted, assuming the attacker can
read the password at physical memory location 0x40:0x1e. It is also
possible for a root user to reboot the computer by instrumenting the BIOS
keyboard buffer in spite of the full disk encryption.

Impact:
1) Plain text password disclosure.
The required privileges to perform this operation are OS dependent, from
unprivileged users under Windows (any), to root under most Unix.

2) A privileged attacker able to write to the MBR and knowing the password
(for instance thanks to 1), is able to reboot the computer in spite of the
password prompted at boot time (and in spite of disk encryption) by
initializing the BIOS keyboard buffer with the correct password (using an
intermediary bootloader that will in turn run DriveCrypt).


ADDITIONAL INFORMATION

The information has been provided by
<mailto:advisories@xxxxxxxxxxxxxxxxxxxxxxx> iViZ Security Advisories.
The original article can be found at:
<http://www.ivizsecurity.com/security-advisory-iviz-sr-0807.html>
http://www.ivizsecurity.com/security-advisory-iviz-sr-0807.html



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