Bypass USB GPO with Mobile Devices

TL;DR

Group Policy Objects (GPOs) applied via USB drives can often be bypassed by mobile devices like iPhones. This is because these devices typically don’t interact with the Windows registry in a way that triggers or respects GPO settings designed for traditional computer connections. This guide explains how this works and what you can do to mitigate the risk.

Understanding the Problem

USB GPOs work by modifying the Windows Registry when a USB drive is connected. Specifically, they target registry keys related to Autorun policies and potentially other settings that control device behaviour. Mobile devices (iPhones, Android phones) generally mount as media devices or use protocols like MTP (Media Transfer Protocol). They don’t execute code in the same way a Windows computer would when interacting with an infected USB drive.

How iPhones Bypass USB GPO

1. No Autorun Execution: iPhones do not automatically run executables or scripts from connected storage devices.
2. Limited Registry Interaction: iPhones don’t directly modify the Windows registry of the host computer when connecting via USB. They primarily transfer files.
3. Protocol Differences: The MTP protocol used by many mobile devices doesn’t trigger GPO updates designed for traditional file system access.

Steps to Verify Bypass (Demonstration)

This section demonstrates how an iPhone will *not* activate a malicious USB GPO.

1. Create a Malicious USB GPO: This is for demonstration purposes only. Do not use this on real systems without explicit permission and in a controlled environment. A simple example might involve creating a registry file to change the default browser.

   Windows Registry Editor Version 5.00
   
   [HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerMain]
   "Start Page"="http://example.com/malicious"
   

2. Save the file as a .reg file (e.g., malicious.reg).
3. Place the .reg file on a USB drive.
4. Connect an iPhone to a Windows computer with GPO enabled for USB drives.
5. Observe: The registry will not be modified when the iPhone is connected. You can verify this by opening the Registry Editor (regedit) and checking the relevant key.

   regedit

Mitigation Strategies

Since mobile devices bypass USB GPOs, focus on preventing malicious USB drive connections in general.

1. Disable Autorun: This is the most effective method. Disable Autorun for all removable drives.
   • Open Group Policy Editor (gpedit.msc).
   • Navigate to Computer Configuration > Administrative Templates > System > Removable Storage Access.
   • Enable “Prevent automatic execution of programs from USB” and “Prevent the use of removable storage media.” Consider setting these policies for all users as well.
2. USB Device Control: Use software that specifically controls which USB devices are allowed to connect.
   • Several third-party solutions offer granular control over USB device access based on vendor ID, product ID, and other criteria.
3. Endpoint Detection and Response (EDR) Solutions: Implement an EDR solution that monitors for suspicious activity related to USB devices.
   • EDR can detect attempts to modify the registry or execute code from USB drives, even if Autorun is disabled.
4. User Education: Train users about the risks of connecting unknown USB drives to company computers.
   • Emphasize that they should never connect a USB drive from an untrusted source.
5. Disable USB Ports (Where Possible): For systems where USB access is not required, consider disabling the ports in the BIOS or through Group Policy.

cyber security Considerations

While iPhones bypass USB GPOs, they are still vulnerable to other attacks. Ensure your mobile device management (MDM) solution is up-to-date and that devices are properly secured with strong passwords and encryption.