Security Advisories

DiskCryptor Security Model bypass exploiting wrong BIOS API usage

Synopsis

The password checking routine of DiskCryptor fails to sanitize the BIOS keyboard buffer before AND after reading passwords.

Affected Software

DiskCryptor 0.2.6 for Windows (possibly other versions also)

Technical Description

DiskCryptor'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 instrument the BIOS keyboard buffer in spite of the full disk encryption.

Impact

1) Plain text password disclosure. Required privileges to perform this operation are OS dependant, 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 keybaord buffer with the correct password (using an intermediary bootloader that will in turn run DiskCryptor).

Full Technical Whitepaper

Technical Whitepaper

Patch Description

Read the detailed fix description

Vendor Response

No Response from vendor in spite of multiple solicitations.

Credits

This vulnerability was discovered by Security Researcher Jonathan Brossard from iViZ Techno Solutions Pvt. Ltd.

Disclosure Timeline

First private disclosure to vendor on July 15th 2008
First Public disclosure at Defcon 16 on August 10th 2008



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