InsydeH2O UEFI Secure Boot Bypass Vulnerability via Digital Certificate Injection

A vulnerability exists in the InsydeH2O UEFI firmware's digital signature verification process. It improperly validates NVRAM variable attributes, allowing an attacker to create a non-authenticated variable that bypasses signature verification. This exploitation enables the execution of arbitrary signed UEFI code, circumventing Secure Boot. The issue arises from the use of an unprotected NVRAM variable, 'SecureFlashCertData', which can be manipulated to inject malicious digital certificates. Once injected, these certificates can be used to execute unsigned or harmful code during the early boot process, before the operating system's security measures are active.

Impact

Exploitation of this vulnerability allows for the injection of digital certificates into the SecureFlashCertData NVRAM variable, bypassing Secure Boot. This could enable the execution of unsigned or malicious UEFI code, potentially leading to the installation of persistent malware or kernel rootkits that survive reboots and OS reinstallations. Such actions could evade detection by endpoint security tools, as they occur before these systems are initialized.

Reproduction

The vulnerability can be reproduced by injecting a digital certificate into the 'SecureFlashCertData' NVRAM variable. This can be done by writing to the variable from an operating system environment, such as Windows or Linux, using administrative privileges. Once the certificate is injected, any UEFI code signed by that certificate can be executed during the boot process, bypassing Secure Boot.

Remediation

Affected UEFI modules should be updated through vendor-provided firmware updates. Due to the vulnerability's presence in multiple PC models, check with the device manufacturer for available patches.