USB Firmware Flashing & Virus Risk

TL;DR

Yes, a program containing a virus can potentially infect a USB drive even during firmware flashing, despite formatting. The risk depends on how the flashing process is handled and where the virus resides within the original file system.

Understanding the Risk

Formatting a USB drive typically removes user-level data, but it doesn’t always erase everything. Firmware areas are often separate from the main filesystem and may not be touched by a standard format. A virus embedded within the boot sector or firmware itself could survive.

Steps to Mitigate Infection Risk

1. Verify the Source of the Firmware File: This is the most important step.
   • Only download firmware from the official manufacturer’s website.
   • Double-check the URL for typos or suspicious characters (e.g., using a known good bookmark).
   • Look for digital signatures on the file to confirm its authenticity. (Not all manufacturers provide this.)
2. Scan with Multiple Antivirus Programs: Before flashing, scan the firmware file (and your computer) with several reputable antivirus programs.
   • Use both online scanners and installed software.
   • Consider using a bootable antivirus rescue disk for a more thorough scan outside of your operating system.
3. Full Format (Not Quick Format): When formatting the USB drive, perform a full format instead of a quick format.
   • A full format overwrites every sector on the drive, increasing the chance of removing any residual virus code.
   • In Windows, uncheck ‘Quick Format’ in the format dialog box.
   • On Linux, use commands like mkfs.fat -F 32 /dev/sdX1 (replace sdX1 with your USB drive’s partition). Be *extremely* careful when using these commands as you can easily wipe the wrong drive!
4. Use a Dedicated Flashing Tool: Use the official flashing tool provided by the manufacturer.
   • These tools are often designed to be more secure and may include checks to prevent malicious firmware from being loaded.
   • Avoid using generic or third-party flashing tools unless you fully trust their source.
5. Bootable USB Creation (If Applicable): If the firmware is intended to be written directly to a boot sector, create a bootable USB drive.
   • Tools like Rufus or Etcher can help with this process.
   • These tools often verify the integrity of the image before writing it to the drive.
6. Isolate the Computer: Disconnect your computer from the internet during the flashing process.
   • This prevents the virus from communicating with a command-and-control server or spreading to other devices.
7. Post-Flash Scan: After flashing, scan the USB drive again with multiple antivirus programs.
   • Also scan your entire computer for any signs of infection.
8. Consider a Low-Level Format (Advanced): For extremely sensitive situations, consider using a low-level format tool.
   • These tools write zeros to every sector on the drive, including firmware areas. Warning: This can damage your USB drive if not done correctly and is generally only recommended for drives you are willing to potentially discard.

Why Formatting Isn’t Always Enough

Viruses can hide in several places that a standard format doesn’t reach:

• Boot Sector: The first sector of the drive, which contains code to start the operating system.
• Master Boot Record (MBR): Similar to the boot sector, but for older systems.
• Firmware Areas: Dedicated sections of the USB drive used by the controller chip.
• Unallocated Space: Remnants of files that may not be completely overwritten during a quick format.

cyber security Best Practices

Regularly update your antivirus software and operating system to protect against new threats. Be cautious when opening attachments or clicking links from unknown sources.