rEDRoviruses – Whether you’re a AV or whether you’re a EDR, You’re stayin’ alive, stayin’ alive…

September 19, 2016 in Anti-*, EDR

EDR software is so hot right now. While AV is mainly focused on badness and silent detections/reputation analysis, the EDR solutions log everything. Sooner or later this ‘everything’ will cause trouble to bad guys and they will act on it. Interestingly, while killing AV doesn’t make that much sense (because it’s so afraid of triggering FPs), the nature and immaturity of EDR (and associated with it an omnipresent problem of dead agents) makes it actually a very easy target…

Such kill-EDR, or at least anti-EDR , or perhaps even just detect-EDR (which already exists) techniques are also important to offensive teams that will surely want to know about the EDR presence and … will try their best to bypass/avoid it…

It’s also important to remember that discussion of anti-EDR is very important for another reason. Most of AV is using anti-tampering technologies that prevent AV from being well… tampered with. EDR should follow these steps closely – otherwise, well… they will be tampered with too. And fundamentally, the more protection and attention is given to the security of EDR – the better. Think of the Project Zero blog that excels in killing bugs in a variety of software ranges – I don’t see any reason why they shouldn’t give it a try with EDR software…

The following is a bunch of ideas that EDR vendors should look into to protect themselves against being shut down:

  • Blocking via Software Restriction Policies
  • Blocking via AppLocker
  • Blocking via Image File Execution Options
    • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
  • Stopping or blocking WMI
    • Many agentless solutions relying on WMI may stop working
  • Disabling Windows Script Host (and VBS/JS) f.ex. via
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows Script Host\Settings\Enabled
    • HKEY_CURRENT_USER\Software\Microsoft\Windows Script Host\Settings\Enabled
      • solutions using visual basic script will stop working – EDR relying on such a single Registry setting needs to ensure this setting is restored prior to execution of every script
  • Disabling the Powershell
  • Changing ACLs to directories/Registry entries
    • Potentially preventing log writing, config updates, etc.
  • Modification of hosts files
    • Same old, same old…
  • Stopping/disabling services
    • I won’t list service names, but they are easy to find
  • Analysis of kernel drivers of EDR solutions may help in finding new ways to escalate privileges

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