Breaking Through Another Side: Bypassing Firmware Security Boundaries from Embedded Controller
summary
Reverse engineering of Lenovo ThinkPad EC firmware (Microchip 16xx family) reveals a static password in the DXE update flow and a race between verify and flash that allows separation of signature checking from the actual flash operation. A crafted BIOS Guard update package (using discovered ipack templates and MSR 0x115/0x116 handoff) enables unsigned EC updates, opening persistent rootkit paths to SPI flash and BIOS. Experiments use IDA Pro and hardware debugging (DCI attempts); replaced ACM caused temporary reboots but systems recoverable.
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chapters (20)
- 0:00Intro
- 2:46Hardware Security Boundaries
- 9:27Methodology
- 11:16EC firmware update process
- 13:24Impact of EC update auth bypass
- 14:52Lenovo Thinkpad EC update header
- 15:16Lenovo Thinkpad EC update process
- 16:39Boot Guard saves the day?
- 17:52Lenovo Thinkpad EC signature check
- 21:56Lenovo disclosure timeline
- 22:20EC take-aways
- 23:21Intel BIOS Guard in a nutshell
- 23:56What is Intel BIOS Guard?
- 26:16Lenovo Thinkpad PFAT update process
- 28:46BIOS Guard hardware support
- 31:59BIOS Guard ACM execution flow
- 33:48BIOS Guard Directory
- 34:29BIOS Guard Platform Data Table
- 36:07BIOS Guard Update Package
- 45:37Signed vs unsigned operations with BIOS Guard script
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