[IVIZ-08-008] LILO Security Model bypass exploiting wrong BIOS API usage

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[ iViZ Security Advisory 08-008 25/08/2008 ]

iViZ Techno Solutions Pvt. Ltd.
http://www.ivizsecurity.com

• Title: LILO Security Model bypass exploiting wrong BIOS API
  usage
• Date: 25/08/2008
• Software: LILO

• –[ Synopsis:

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

• –[ Affected Software:

  • LILO 22.6.1 (current) and all previous versions

• –[ Technical description:

  LILO'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.
  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 LILO).

• –[ Full Technical Whitepaper

  http://www.ivizsecurity.com/research/preboot/preboot_whitepaper.pdf

• –[ Vendor response:

  • No Response from author in spite of multiple solicitations.

  • [email protected] has been intimated and distribution makers are
    working on separate fixes.

• –[ 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
  • Contacted [email protected] on July 29th 2008
  • First Public disclosure at Defcon 16 on August 10th 2008

• –[ Reference:

  http://www.ivizsecurity.com/security-advisory.html
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