How to Bypass Verified Boot Security in Chromium OS

TL;DR

This paper reveals a design flaw in Chromium OS's verified boot that allows attackers to replace the root filesystem with malicious versions, bypassing security and enabling data theft, with proposed mitigation strategies.

Contribution

The paper uncovers a vulnerability in Chromium OS's verified boot and demonstrates practical attacks, along with mitigation techniques to enhance security.

Findings

Attack successfully replaces rootfs with malicious version

Spyware can extract encrypted user data in plaintext

Mitigation strategies can prevent the exploit

Abstract

Verified boot is an interesting feature of Chromium OS that supposedly can detect any modification in the root file system (rootfs) by a dedicated adversary. However, by exploiting a design flaw in verified boot, we show that an adversary can replace the original rootfs by a malicious rootfs containing exploits such as a spyware or keylogger and still pass the verified boot process. The exploit is based on the fact that a dedicated adversary can replace the rootfs and the corresponding verification information in the bootloader. We experimentally demonstrate an attack using both the base and developer version of Chromium OS in which the adversary installs a spyware in the target system to send cached user data to the attacker machine in plain text which are otherwise encrypted, and thus inaccessible. We also demonstrate techniques to mitigate this vulnerability.