Pre-OS Boot × Insyde H2O UEFI-compatible firmware

vulnerability in Insyde H2O UEFI firmware allows an attacker with local admin access to bypass Secure Boot

The attacker generates a self-signed certificate, wraps it in EFI_SIGNATURE_LIST format, and writes it to the non-volatile NVRAM variable 'SecureFlashCertData' while setting 'SecureFlashSetupMode' to 1. This causes the firmware to trust binaries signed with the attacker's certificate as if they were signed by Insyde. During a firmware update, the attacker replaces the legitimate flasher 'isflash.bin' with a malicious one signed with their certificate. The firmware's SecureFlashDxe driver loads and executes this malicious flasher, granting code execution with write access to firmware volumes not protected by Intel BootGuard or a properly configured FlashDeviceMap.

Monitor firmware integrity using hardware root-of-trust attestation (e.g., Intel BootGuard, TPM PCR measurements) and compare against known-good firmware hashes. Enforce strict FlashDeviceMap configurations that prevent runtime DXE volume modification, and audit NVRAM variable changes (especially SecureFlashCertData and SecureFlashSetupMode) via UEFI event logs or endpoint telemetry.