Attack Chain

1. Attacker gains initial access to the system (physical access or remote access via another vulnerability).
2. Attacker modifies the grub.cfg file, the main configuration file for GRUB2, either directly or indirectly through other system vulnerabilities.
3. The modified grub.cfg introduces malicious code or configurations exploiting a GRUB2 vulnerability.
4. The system is rebooted, triggering the GRUB2 bootloader.
5. GRUB2 parses the malicious configuration in grub.cfg.
6. Due to the vulnerability, the malicious code is executed with elevated privileges, allowing arbitrary code execution.
7. Alternatively, the malicious configuration triggers a denial-of-service condition within GRUB2, causing a system crash or preventing the boot process from completing.
8. The attacker achieves arbitrary code execution at the bootloader level or renders the system unusable.

Impact

Successful exploitation of these vulnerabilities can lead to complete system compromise, as the attacker gains control over the boot process. This can allow for the installation of rootkits, bypass of security measures, and exfiltration of sensitive data. Furthermore, a denial-of-service attack can render systems unusable, leading to data loss and business disruption. The lack of specific victim data prevents quantification, but the potential impact is significant for any system relying on GRUB2.

Recommendation

• Implement file integrity monitoring on /boot/grub/grub.cfg and other GRUB2 configuration files to detect unauthorized modifications (reference: Attack Chain step 2 and file_event log source).
• Deploy the provided Sigma rules to detect suspicious process executions that could indicate attempts to modify GRUB2 configuration files (reference: rules section).
• Regularly audit and update GRUB2 installations to the latest patched version to mitigate known vulnerabilities (reference: Overview section).