Microsoft Copilot triggers Surface bricking bug; firmware patch underway

Microsoft has been quietly patching a firmware flaw in Surface devices that allowed attackers to permanently brick the hardware with a single packet, but only if Secure Core and Secure Boot are disabled. The vulnerability was discovered inadvertently when Microsoft Copilot AI generated a Python script that rendered a security researcher's laptop inoperable.

The bug was identified by Jack Darcy, an Australian security researcher, whose instance of Microsoft Copilot created and executed four Python scripts while probing for backlight control values on a Surface device. The scripts sent raw SSAM ioctl commands to the SAM microcontroller through the SAM software path, overwriting the embedded controller firmware and bricking the device permanently.

How the SAM firmware flaw allows persistent bricking

The SAM (Surface SAM microcontroller) is the embedded controller used in all Surface devices. Darcy told The Register that Microsoft's implementation lacks any defense against arbitrary write values. Typically, digital devices require pressing a button or connecting a jumper to enable arbitrary write access, but that security check is absent in Surface hardware.

Without Secure Core and Secure Boot protections, a single probing script can trigger an update command from the SAM that overwrites both the UEFI and Secure Boot firmware. The device continues operating until reboot, when the SAM fails to initialize and the system cannot Power-On Self-Test. The result is a permanently bricked device with no USB recovery, no factory reset, and no access to BIOS or UEFI. Repair requires a new motherboard at hundreds of dollars cost.

• Flaw exists in all Surface devices with the SAM microcontroller
• Exploit requires administrator privileges and Secure Boot disabled
• Copilot AI accidentally discovered the bug during backlight control probing
• Microsoft has been patching affected devices for the past 90 days
• Permanently bricked devices have no recovery path without motherboard replacement

Microsoft downplays risk, researcher says otherwise

Microsoft does not consider the bug a practical threat. A company spokesperson told The Register that an attacker would need administrator privileges and must disable Secure Boot to exploit it. The spokesperson added that with such access, attackers could perform many other actions.

Darcy countered that the SAM Bus design is fundamentally flawed. Command IDs for read and write operations are interleaved in the same numbering space, meaning any probe that scans two consecutive CIDs has a coin-flip chance of triggering a destructive write. He said there is no safe range to probe, and scanning the bus inevitably kills the unit. Microsoft declined to comment on whether the design will be revised in future Surface hardware. The patch rollout is expected to complete within 30 days.