Pre-OS Boot (T1542)
Pre-OS Boot [T1542]
Last updated
Pre-OS Boot [T1542]
Last updated
Name: Pre-OS Boot
ID: T1542
Tactics: ,
Sub-Technique: , , , ,
Pre-OS Boot techniques, as classified under MITRE ATT&CK (T1542), involve adversaries executing malicious code or modifying system components before the operating system fully boots. Such methods allow attackers to maintain persistence, evade detection, and establish deep-rooted control over compromised systems. These techniques primarily target firmware, bootloaders, and other pre-operating system components to ensure malicious code execution at the earliest stages of system startup.
Pre-OS Boot attacks exploit vulnerabilities or weaknesses in the system boot process, firmware, or hardware initialization routines. Attackers typically leverage the following methods:
Firmware Modification:
Manipulating BIOS or UEFI firmware to embed malicious code.
Utilizing firmware rootkits to persistently infect systems, surviving OS reinstallations or disk replacements.
Bootloader Manipulation:
Altering bootloader code (e.g., GRUB, Windows Boot Manager) to execute malicious payloads before the OS loads.
Injecting code into boot sectors or EFI partitions.
Hardware-Level Attacks:
Exploiting vulnerabilities in hardware components (chipsets, TPM, storage controllers) to execute malicious instructions pre-boot.
Using compromised hardware or firmware implants to subvert system security.
Secure Boot Bypass:
Exploiting vulnerabilities or misconfigurations to bypass secure boot mechanisms, enabling unauthorized code execution at boot time.
Employing stolen or compromised signing keys to sign malicious bootloaders or firmware.
Real-world procedures typically involve:
Gaining initial system access through phishing, supply chain compromise, or physical access.
Escalating privileges to modify firmware or bootloader components.
Installing persistent implants or rootkits to ensure stealth and longevity.
Attackers commonly employ Pre-OS Boot techniques in the following scenarios and stages of an attack:
Persistence Stage:
To maintain long-term, stealthy persistence that survives OS reinstallation, system updates, and security software scans.
Privilege Escalation:
To escalate privileges by controlling system boot processes and firmware-level operations, enabling attackers to bypass OS-level security controls.
Defense Evasion:
To evade detection by security solutions that typically operate at OS-level, as pre-OS boot code executes before security tools are active.
Supply Chain Attacks:
Embedding malicious firmware or bootloader modifications during hardware manufacturing or software distribution processes.
Advanced Persistent Threat (APT) Operations:
Leveraging pre-OS malware to maintain persistent access in high-value targets, including government agencies, critical infrastructure, and large enterprises.
Physical Access Scenarios:
Exploiting systems where an attacker has temporary physical access, enabling direct firmware manipulation or bootloader tampering.
Detection of Pre-OS Boot compromises typically requires specialized methods, tools, and indicators of compromise (IoCs):
Firmware Integrity Checks:
Regularly verifying firmware integrity through cryptographic hashes, secure boot procedures, and firmware attestation tools.
Bootloader Monitoring:
Analyzing bootloader configurations, boot sectors, EFI partitions, and monitoring for unauthorized modifications or anomalies.
Hardware Security Modules (HSM) and TPMs:
Utilizing Trusted Platform Modules (TPMs) or hardware security modules to detect deviations from expected boot measurements and firmware states.
UEFI Scanning Tools:
Employing specialized tools such as CHIPSEC, UEFITool, or ESET UEFI Scanner to detect malicious firmware implants or unauthorized code injections.
Behavioral Indicators:
Unexpected system crashes or boot failures.
Unusual boot times or delays.
Unrecognized firmware version numbers or unexpected firmware updates.
Specific Indicators of Compromise (IoCs):
Unknown or unsigned firmware images.
Suspicious EFI binaries or bootloader files.
Unusual firmware or bootloader configurations detected in logs.
Detecting Pre-OS Boot techniques is critical due to their severe impact on systems and networks:
High-Level Persistence:
Malicious firmware implants or bootloader modifications persist across OS reinstallation, disk replacement, and routine security updates, making remediation challenging.
Stealth and Evasion:
Pre-OS malware executes before OS-level security controls are active, significantly reducing detection chances and allowing attackers prolonged undetected presence.
Privilege Escalation and Control:
Attackers gain comprehensive control over system initialization, enabling high-level privilege escalation and potential system compromise at the deepest hardware and firmware levels.
Integrity and Availability Risks:
Malicious pre-OS code can compromise system integrity, causing instability, data corruption, or denial-of-service conditions.
Supply Chain Risks:
Pre-OS attacks embedded during manufacturing or distribution can affect large-scale deployments, impacting numerous systems simultaneously.
Early detection and mitigation of Pre-OS Boot compromises are essential to prevent long-term damage, reduce remediation costs, and maintain system integrity and trustworthiness.
Real-world examples of Pre-OS Boot attacks include:
LoJax UEFI Rootkit (APT28):
Attack Scenario: Russian-linked threat actor APT28 compromised UEFI firmware to install LoJax, establishing persistent access on targeted systems.
Tools Used: LoJax malware, firmware flashing tools, compromised legitimate utilities.
Impact: Persistent, stealthy infection surviving OS reinstallations, enabling long-term espionage operations.
MosaicRegressor UEFI Malware (APT41):
Attack Scenario: Chinese-linked APT41 utilized MosaicRegressor, a malicious UEFI implant, to target diplomatic entities.
Tools Used: MosaicRegressor malware, firmware exploitation, and modification tools.
Impact: Persistent espionage campaigns with deep system-level access, difficult to detect and remediate.
TrickBoot Module (TrickBot Malware):
Attack Scenario: TrickBot operators developed TrickBoot to inspect UEFI firmware vulnerabilities, potentially enabling firmware-level persistence.
Tools Used: TrickBot malware framework, TrickBoot module.
Impact: Potential for firmware-level persistence, significantly complicating remediation and detection efforts.
Sednit Group (APT28) Secure Boot Bypass:
Attack Scenario: Exploiting vulnerabilities in Secure Boot implementations to load unsigned malicious bootloaders.
Tools Used: Custom bootloader modifications, exploitation of Secure Boot vulnerabilities.
Impact: Complete bypass of fundamental security controls, enabling persistent, stealthy malware execution.
These examples illustrate the severity and persistence potential of Pre-OS Boot attacks, highlighting the necessity for robust detection and mitigation strategies.