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ExpoMon

ExpoMon is a plugin developed by milCERT.ch, the Swiss Military CERT, for x64dbg with the goal to assist a reverse engineer during dynamic analysis of malicious binaries when they resolve APIs, e.g. with functions such as GetProcAddress, LdrGetProcedureAddress, etc. or a custom implementation of those functions. In theory, the plugin monitors access to a module's IMAGE_EXPORT_DIRECTORY.AddressOfFunctions array, which is usually accessed when resolving an exported function's address via the Export Address Table (EAT); in practice, in favor of increased performance, the plugin monitors access to a cloned page of the memory page containing the module's EAT with IMAGE_EXPORT_DIRECTORY.AddressOfFunctions hijacked to point to it.

Features

• Logs context information on access to the address containing the RVA of an exported function
• Hijacks the accessed exported functions (RVA hijack)

Known limitations (by design)

• Cannot handle cases where pattern scanning is used to find the functions
• Cannot handle cases where hardcoded relative offsets are used to find the functions
• Cannot handle direct syscalls

Install

• Download or compile the plugin
  • Compiled with
    • Visual Studio 2013 with Qt Visual Studio Tools version 2.3.2
    • Qt 5.6.3 (x64/x86 msvc2013)
    • Qt Creator 4.3.1
• Copy the plugin to the plugins directory
  • release\x64\plugins\ExpoMon.dp64
  • release\x32\plugins\ExpoMon.dp32
• Set or add MembpAlt=1 to the [Engine] section in x64dbg.ini
  • This configures memory breakpoints to use PAGE_NOACCESS instead of PAGE_GUARD

Usage

• If it is not visiable in the tabs

  • Plugins > ExpoMon > Show

• To enable the exports monitoring: Monitor Exports

  • This will monitor the access to the exports of all the currently loaded modules
    • In the Settings tab it is possible to configure to only monitor specific modules
  • Modules that are loaded at a later stage are also automatically monitored (CB_LOADDLL / LOAD_DLL_DEBUG_EVENT)

• To temporarily disable any monitoring: Disable Monitoring

  • Internally executes the DisableMemoryBreakpoint command on every monitored memory page

• To completely remove and disable the monitoring: Reset

  • This may potentially lead to a crash / unhandled exceptions, due to the fact that there may still be pointers in use to the monitored pages, which will be freed, causing invalid memory access

• In the Settings tab it is possible to configure the conditions for breaking and hijacking

  • The conditions use the internal scripting engine (https://help.x64dbg.com/en/latest/introduction/index.html)
  • Module and function names can be separated by a , and ; or a newline
    • The check performs an needle/substring search so that adding file extensions is not required

Screenshots

License

MIT License