Corey Kallenberg, John Butterworth, Xeno Kovah (The MITRE Corporation)

PRESENTATION TITLE: Defeating Signed BIOS Enforcement

PRESENTATION ABSTRACT:

The integrity of the BIOS is paramount to the security of the platform. Research such as “BIOS Chronomancy” shows that an attacker who exists in the BIOS can evade detection by the Trusted Platform Module and even survive BIOS reflashing attempts. Furthermore, Invisible Things Labs showed in “Attacking Intel Trusted Execution Technology” that a System Management Mode (SMM) present malware can interfere with TXT execution.

As it is the BIOS that initially configures SMM, it follows that BIOS control implies SMM control. However, as we will see, SMM control *can* also imply BIOS control. The central role of the BIOS in the platform’s security, as well as the need to patch the BIOS with legitimate vendor updates poses an interesting problem. The most common solution that vendors adopt to solve this problem is to utilize Intel architecture flash-chip protection mechanisms to provide a BIOS update routine that verifies the signature on an incoming update before writing the update to the BIOS.

In this secure BIOS update scheme, there are two primary attack surfaces that can be targeted in an attempt to break the signed BIOS requirement: the Intel architecture protection mechanisms, and the vendor’s implementation of the signature enforcement and update routine. This presentation demonstrates two attacks; one against each of these targets. Both of these attacks allow an attacker to arbitrarily re-flash the BIOS on a number of systems despite the presence of signed BIOS enforcement.

ABOUT COREY KALLENBERG

Corey Kallenberg is a security researcher currently employed by The MITRE Corporation. Corey specializes in low level system development, vulnerability discovery and exploitation, and rootkit analysis. Corey’s current focus is on BIOS/UEFI security. Corey has previously presented his research at DEFCON, Blackhat USA, IEEE S&P and NoSuchCon.

ABOUT JOHN BUTTERWORTH

John Butterworth is a security researcher at The MITRE Corporation who specializes in low level system security. He is applying his electrical engineering background and firmware engineering background to investigate UEFI/BIOS security.

ABOUT XENO KOVAH

Xeno is a Lead InfoSec Engineer at The MITRE Corporation, a non-profit company that runs 6 federally funded research and development centers (FFRDCs) as well as manages CVE. He is the team lead for the BIOS Analysis for Detection of Advanced System Subversion project. On the predecessor project, Checkmate, he investigated kernel/userspace memory integrity verification & timing-based attestation. Both projects have a special emphasis on how to make it so that the measurement agent can’t just be made to lie by an attacker.