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Copy file name to clipboardExpand all lines: _posts/2025-12-15-silver-fox-poc-2025.md
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@@ -46,8 +46,8 @@ The Python community has provided a ready-made library: [PythonMemoryModule](htt
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After importing this library, any DLL/EXE can be loaded into the memory of the `python.exe` host process.
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> [!NOTE]
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> After local testing, EXEs compiled with C/C++ run perfectly, but .NET programs do not work properly.
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{: .prompt-tip }
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```python
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import pythonmemorymodule
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The open-source project [EDRSilencer](https://github.com/netero1010/EDRSilencer) was born based on this principle. Released in late 2023, this tool aims to set WFP filters against EDR/AV processes, thereby blocking their communication with the cloud and preventing them from reporting threat information. SilverFox variants in 2025 also adopted the exact same method.
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> [!NOTE]
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> To evade detection, the author of EDRSilencer implemented the `FwpmGetAppIdFromFileName0` function themselves, avoiding direct calls to `CreateFileW`, thus successfully bypassing Minifilter monitoring.
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Below are code snippets based on the core logic of EDRSilencer, showing how to configure WFP filters to block traffic for specific processes:
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1.`IOCTL_REGISTER_PROCESS` has a serious logic flaw; any process can register its PID to the whitelist, **with absolutely no permission validation**.
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> At this point, this driver can successfully run on the latest Windows 11 machines with HVCI (Hypervisor-Protected Code Integrity) enabled.
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Below is the key code snippet of the POC:
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Its core logic lies in **communicating directly via RPC**, thereby bypassing high-level Win32 APIs.
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> [!NOTE]
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> Typically, EDR/AV products hook standard APIs like `OpenSCManager()` or `CreateService()` to monitor service creation behavior. CreateSvcRpc does not call these APIs but communicates directly with the SCM's RPC interface via named pipes, manually constructing DCE/RPC protocol packets. This method effectively evades detection mechanisms based on API Hooking.
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### RPC Protocol Implementation Details
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In late 2024, security researchers **Jonathan Beierle** and **Logan Goins** published an article titled [Weaponizing WDAC - Killing the Dreams of EDR](https://beierle.win/2024-12-20-Weaponizing-WDAC-Killing-the-Dreams-of-EDR/), detailing how to abuse the WDAC mechanism to disable the operation of antivirus software and EDR.
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> [!NOTE]
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> The core key point of this attack method is: **WDAC policies have a higher loading priority than EDR drivers during the system boot phase**.
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### Attack Process
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3. Map an unused drive letter (e.g., `X:`) to the system's Common Start Menu `Programs` directory by writing a new value to the `DOS Devices` key under `Session Manager`.
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> [!NOTE]
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> This mapping does not take effect immediately but is processed by the Session Manager (SMSS) at the next system boot.
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4. The attacker writes a pair of paths to the `PendingFileRenameOperations` registry value. The source path is the file with the random extension created earlier, and the target path uses the virtual drive letter just mapped plus the `Startup` subdirectory (e.g., `X:\Startup\reboot.qmtk`).
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> [!TIP]
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> This registry value is specifically used to record file operations that need to be performed upon reboot (commonly used for Windows updates or driver installations).
The evolution of evasion techniques demonstrated by the SilverFox Trojan in 2025 marks that the investment of black market groups in endpoint confrontation has reached a quasi-APT level. From using native system mechanisms like WFP and WDAC to "borrow a knife to kill" and disable security software, to mining obscure RPC interfaces to bypass Hooks and load drivers, to using BYOVD technology to directly counter EDR at the kernel layer through vulnerable drivers, these methods all show the attacker's profound understanding of the underlying mechanisms of the Windows operating system. It is particularly noteworthy that SilverFox disguises attack behaviors as legitimate system management operations (such as configuring firewall rules, application control policies, registry file operations, etc.). This "Living off the Land" approach greatly increases the difficulty of detection, and traditional defense means based on signatures or single behaviors are no longer effective.
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> [!NOTE]
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> For the Blue Team, this means not only focusing on file-level threats but also strengthening monitoring of system configuration changes, abnormal driver loading, and abnormal behaviors of legitimate processes. Attack and defense confrontation is a never-ending game. In-depth study of the implementation details of these frontier samples is the only way to improve the resilience of the defense system.
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