预操作系统引导攻击指攻击者通过篡改系统固件或引导过程在操作系统加载前植入恶意代码，建立超越操作系统权限的持久化控制。此类攻击直接操作硬件层组件，可绕过传统基于操作系统的安全防护。防御措施主要包括固件完整性校验、安全启动机制强化、NVRAM变更监控等，通过可信平台模块（TPM）度量引导过程和定期固件健康检查进行威胁发现。
为规避固件层安全检测机制，攻击者发展出多维度匿迹技术，通过硬件级代码隐匿、动态策略篡改和存储介质创新利用，将恶意行为深度嵌入系统初始化环节，构建出"固件融合、时序规避"的新型持久化攻击范式。
现有预操作系统引导匿迹技术的核心特征表现为硬件层操作与瞬时性攻击的结合。固件级代码注入通过芯片级存储介质篡改，将恶意代码植入固件验证边界之外，利用硬件-软件监控断层实现隐匿；安全启动动态旁路技术聚焦UEFI安全机制的瞬时穿透，在维持系统表面完整性的前提下完成恶意负载加载；NVRAM隐蔽存储则开辟独立于磁盘文件的持久化新维度。三类技术的共性在于突破传统持久化攻击的存储介质局限，通过硬件资源滥用、固件机制逆向和瞬时状态篡改，将攻击痕迹分散在多个不可见层级。其技术演进呈现出从静态存储向动态加载、从永久修改向瞬时注入的发展趋势，显著增加了防御方进行攻击取证和逆向分析的难度。
匿迹技术的升级迫使防御体系向硬件安全层延伸，需构建固件运行时监控、NVRAM行为基线分析等新型防御能力，研发基于物理信号侧信道分析的硬件异常检测技术，并建立跨厂商的固件完整性验证标准，以应对预引导阶段的深度隐匿威胁。
| 效应类型 | 是否存在 |
|---|---|
| 特征伪装 | ✅ |
| 行为透明 | ✅ |
| 数据遮蔽 | ✅ |
| 时空释痕 | ❌ |
攻击者通过仿冒合法固件模块的数字签名，将恶意代码伪装成经过验证的硬件驱动或系统组件。利用UEFI模块化设计特性，将攻击载荷嵌入具有合法厂商签名的固件更新包，使得恶意模块具备表面合法性，规避基于签名验证的防护机制。
通过直接操作硬件层的中断处理机制（如系统管理中断SMI），在操作系统不可见的特权层级执行恶意代码。该手法利用处理器特权级隔离特性，使得恶意活动完全绕过操作系统级的行为监控，实现"零进程、零线程"的透明化攻击。
采用芯片级加密存储和运行时动态解密技术，确保恶意载荷在非易失存储器中始终处于加密状态。通过硬件安全区域（如TPM）托管解密密钥，结合固件更新流程的加密通信通道，使得静态固件分析难以提取有效攻击指纹。 该技术通过硬件层特征伪装实现恶意代码合法化，利用特权级隔离达成行为不可见性，并借助硬件加密机制完成数据遮蔽，形成多维度的匿迹防护体系。其技术特性导致传统基于软件层的安全检测完全失效，需从硬件信号监测和固件行为建模等新维度构建防御体系。
| ID | Mitigation | Description |
|---|---|---|
| M1047 | Audit |
Perform audits or scans of systems, permissions, insecure software, insecure configurations, etc. to identify potential weaknesses. |
| M1046 | Boot Integrity |
Use Trusted Platform Module technology and a secure or trusted boot process to prevent system integrity from being compromised. Check the integrity of the existing BIOS or EFI to determine if it is vulnerable to modification. [1] [2] |
| M1035 | Limit Access to Resource Over Network |
Prevent access to file shares, remote access to systems, unnecessary services. Mechanisms to limit access may include use of network concentrators, RDP gateways, etc. |
| M1026 | Privileged Account Management |
Ensure proper permissions are in place to help prevent adversary access to privileged accounts necessary to perform these actions |
| M1051 | Update Software |
Patch the BIOS and EFI as necessary. |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0017 | Command | Command Execution |
Monitor executed commands and arguments in command history in either the console or as part of the running memory to determine if unauthorized or suspicious commands were used to modify device configuration. |
| DS0016 | Drive | Drive Modification |
Monitor for changes to MBR and VBR as they occur for indicators for suspicious activity and further analysis. Take snapshots of MBR and VBR and compare against known good samples. |
| DS0027 | Driver | Driver Metadata |
Disk check, forensic utilities, and data from device drivers (i.e. processes and API calls) may reveal anomalies that warrant deeper investigation |
| DS0001 | Firmware | Firmware Modification |
Monitor for changes made on pre-OS boot mechanisms that can be manipulated for malicious purposes. Take snapshots of boot records and firmware and compare against known good images. Log changes to boot records, BIOS, and EFI |
| DS0029 | Network Traffic | Network Connection Creation |
Monitor for newly constructed network device configuration and system image against a known-good version to discover unauthorized changes to system boot, startup configuration, or the running OS. The same process can be accomplished through a comparison of the run-time memory, though this is non-trivial and may require assistance from the vendor. |
| DS0009 | Process | OS API Execution |
Monitor for API calls that may abuse Pre-OS Boot mechanisms as a way to establish persistence on a system. Disk check, forensic utilities, and data from device drivers (i.e. API calls) may reveal anomalies that warrant deeper investigation. [3] |