修改系统镜像指攻击者通过篡改嵌入式设备的操作系统镜像文件，持久化植入恶意功能或削弱设备安全机制的入侵行为。传统防御主要依赖固件完整性校验、数字签名验证、运行时内存保护等技术，通过比对官方镜像哈希值、验证更新包签名、监控内存异常修改等手段进行防护。典型缓解措施包括建立可信固件库、实施双因子更新认证、部署内存完整性验证系统等。
为规避传统检测机制，攻击者发展出多维度匿迹篡改技术。通过将恶意代码植入固件深层结构、利用内存动态修改保持存储介质洁净、劫持官方更新通道实现合法化部署，以及构建实时校验欺骗系统等手段，使得镜像篡改行为在静态存储、动态运行、传输过程等环节均具备高度隐蔽性。
现有匿迹技术的核心特征体现在对设备信任链的全周期渗透。固件级隐蔽植入突破存储介质防护，利用固件结构特性实现物理级隐匿；内存驻留篡改技术创造瞬时攻击范式，规避持久化特征留存；合法更新劫持技术逆向利用设备安全更新机制，将攻击行为转化为"合法"运维操作；动态校验和绕过构建实时欺骗系统，瓦解完整性验证的防御价值。这些技术的共性在于精确把握设备安全机制的盲区，通过"寄生"于合法流程、"融合"于系统特性、"同步"于校验机制等策略，实现镜像篡改行为的深度隐匿。
匿迹技术的发展导致传统基于静态特征检测、单向校验验证的防护体系面临失效风险，防御方需构建固件行为动态基线分析、更新包全生命周期追溯、内存-存储交叉验证等新型检测能力，并引入供应链安全验证机制，建立覆盖镜像全生命周期的可信执行环境。
| 效应类型 | 是否存在 |
|---|---|
| 特征伪装 | ✅ |
| 行为透明 | ✅ |
| 数据遮蔽 | ✅ |
| 时空释痕 | ❌ |
攻击者通过精确复现官方镜像的文件结构和数字签名，使篡改后的系统镜像在格式特征、证书链验证等维度与合法镜像完全一致。利用设备制造商的标准更新协议封装恶意载荷，使得篡改行为在传输过程、安装日志等环节均呈现合法特征。
通过零日漏洞利用实现无痕内存修改，或借助供应链攻击获取合法签名密钥，使得镜像篡改过程不触发任何异常日志或安全告警。攻击者利用设备自身的安全机制缺陷，使恶意操作被系统误判为正常功能调用。
采用固件级加密存储和动态解密加载技术，将恶意代码以密文形式嵌入系统镜像的保留区域。在设备运行时通过硬件级解密模块实时解密执行，使得静态取证分析无法获取有效攻击载荷。
| ID | Mitigation | Description |
|---|---|---|
| M1046 | Boot Integrity |
Some vendors of embedded network devices provide cryptographic signing to ensure the integrity of operating system images at boot time. Implement where available, following vendor guidelines. [1] |
| M1045 | Code Signing |
Many vendors provide digitally signed operating system images to validate the integrity of the software used on their platform. Make use of this feature where possible in order to prevent and/or detect attempts by adversaries to compromise the system image. [2] |
| M1043 | Credential Access Protection |
Some embedded network devices are capable of storing passwords for local accounts in either plain-text or encrypted formats. Ensure that, where available, local passwords are always encrypted, per vendor recommendations. [3] |
| M1032 | Multi-factor Authentication |
Use multi-factor authentication for user and privileged accounts. Most embedded network devices support TACACS+ and/or RADIUS. Follow vendor prescribed best practices for hardening access control.[4] |
| M1027 | Password Policies |
Refer to NIST guidelines when creating password policies. [5] |
| M1026 | Privileged Account Management |
Restrict administrator accounts to as few individuals as possible, following least privilege principles. Prevent credential overlap across systems of administrator and privileged accounts, particularly between network and non-network platforms, such as servers or endpoints. |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0022 | File | File Modification |
Most embedded network devices provide a command to print the version of the currently running operating system. Use this command to query the operating system for its version number and compare it to what is expected for the device in question. Because this method may be used in conjunction with Patch System Image, it may be appropriate to also verify the integrity of the vendor provided operating system image file. Compare the checksum of the operating system file with the checksum of a known good copy from a trusted source. Some embedded network device platforms may have the capability to calculate the checksum of the file, while others may not. Even for those platforms that have the capability, it is recommended to download a copy of the file to a trusted computer to calculate the checksum with software that is not compromised. [6] Many vendors of embedded network devices can provide advanced debugging support that will allow them to work with device owners to validate the integrity of the operating system running in memory. If a compromise of the operating system is suspected, contact the vendor technical support and seek such services for a more thorough inspection of the current running system. [7] |