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Yesterday, a group of European information security researchers announced that they have discovered a vulnerability in Intel’s Management Engine (Intel ME) INTEL-SA-00086. They say that the root of this problem is an undocumented Intel ME mode, specifically known as the Manufacturing Mode.

Undocumented commands enable overwriting SPI flash memory and implementing the doomsday scenario. The vulnerability could locally exploit of an ME vulnerability (INTEL-SA-00086).

What is Manufacturing Mode?

Intel ME Manufacturing Mode is intended for configuration and testing of the end platform during manufacturing. However, this mode and its potential risks are not described anywhere in Intel’s public documentation.

Ordinary users do not have the ability to disable this mode since the relevant utility (part of Intel ME System Tools) is not officially available. As a result, there is no software that can protect, or even notify, the user if this mode is enabled.

This mode allows configuring critical platform settings stored in one-time-programmable memory (FUSEs). These settings include those for BootGuard (the mode, policy, and hash for the digital signing key for the ACM and UEFI modules). Some of them are referred to as FPFs (Field Programmable Fuses).

An output of the -FPFs option in FPT

In addition to FPFs, in Manufacturing Mode the hardware manufacturer can specify settings for Intel ME, which are stored in the Intel ME internal file system (MFS) on SPI flash memory. These parameters can be changed by reprogramming the SPI flash. The parameters are known as CVARs (Configurable NVARs, Named Variables). CVARs, just like FPFs, can be set and read via FPT.

Manufacturing mode vulnerability in Intel chips within Apple laptops

The researchers analyzed several platforms from a number of manufacturers, including Lenovo and Apple MacBook Prо laptops. The Lenovo models did not have any issues related to Manufacturing Mode. However, they found that the Intel chipsets within the Apple laptops are running in Manufacturing Mode and was found to include the vulnerability CVE-2018-4251.

This information was reported to Apple and the vulnerability was patched in June, in the macOS High Sierra update 10.13.5.

By exploiting CVE-2018-4251, an attacker could write old versions of Intel ME (such as versions containing vulnerability INTEL-SA-00086) to memory without needing an SPI programmer and without physical access to the computer.

Thus, a local vector is possible for exploitation of INTEL-SA-00086, which enables running arbitrary code in ME.

The researchers have also stated, in the notes for the INTEL-SA-00086 security bulletin, Intel does not mention enabled Manufacturing Mode as a method for local exploitation in the absence of physical access. Instead, the company incorrectly claims that local exploitation is possible only if access settings for SPI regions have been misconfigured.

How can users save themselves from this vulnerability?

To keep users safe, the researchers decided to describe how to check the status of Manufacturing Mode and how to disable it.

Intel System Tools includes MEInfo in order to allow obtaining thorough diagnostic information about the current state of ME and the platform overall.

They demonstrated this utility in their previous research about the undocumented HAP (High Assurance Platform) mode and showed how to disable ME. The utility, when called with the -FWSTS flag, displays a detailed description of status HECI registers and the current status of Manufacturing Mode (when the fourth bit of the FWSTS status register is set, Manufacturing Mode is active).

Example of MEInfo output

They also created a program for checking the status of Manufacturing Mode if the user for whatever reason does not have access to Intel ME System Tools. Here is what the script shows on affected systems:

mmdetect script

To disable Manufacturing Mode, FPT has a special option (-CLOSEMNF) that allows setting the recommended access rights for SPI flash regions in the descriptor.

Here is what happens when -CLOSEMNF is entered:

Process of closing Manufacturing Mode with FPT

Thus, the researchers demonstrated that Intel ME has a Manufacturing Mode problem. Even major commercial manufacturers such as Apple are not immune to configuration mistakes on Intel platforms. Also, there is no public information on the topic, leaving end users in the dark about weaknesses that could result in data theft, persistent irremovable rootkits, and even ‘bricking’ of hardware.

To know about this vulnerability in detail, visit Positive research’s blog.

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