LILO Security Model bypass exploiting wrong BIOS API usage

Risk: Low
Local: Yes
Remote: No
CWE: CWE-200

CVSS Base Score: 2.1/10
Impact Subscore: 2.9/10
Exploitability Subscore: 3.9/10
Exploit range: Local
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: None
Availability impact: None

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 - ----------------------------------------------------------------------- [ iViZ Security Advisory 08-008 25/08/2008 ] - ----------------------------------------------------------------------- iViZ Techno Solutions Pvt. Ltd. - ----------------------------------------------------------------------- * 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 - --[ Vendor response: * No Response from author in spite of multiple solicitations. * vendor-sec (at) lst (dot) de [email concealed] 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 vendor-sec (at) lst (dot) de [email concealed] on July 29th 2008 * First Public disclosure at Defcon 16 on August 10th 2008 - --[ Reference: -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) iD8DBQFIsngtkcchhz1mT/IRAgcBAKDDFnYFqZz7Oo8LKnbxjI48vLbyuQCeLFkv ilcv/NIQZpoBZlr66Gu62GI= =tSJc -----END PGP SIGNATURE-----


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