Security Week 47: Bypassing Computer Sleep Protection

November 10 Intel patched vulnerability CVE-2020-8705 in the Intel Boot Guard mechanism, which allows you to bypass key protection methods of the computer while it is in sleep mode. Vulnerability in detail describes researcher Trammell Hudson. He gives a realistic attack scenario that requires physical access to the hardware and includes flashing the BIOS chip.

Intel Boot Guard technology is designed to exclude such attacks: in theory, it ensures that only trusted code is loaded at the initial stage of turning on the computer. As it turns out, when the computer wakes up from S3 sleep, not all devices authenticate the contents of the flash memory, which allows you to change the code. The consequences of such an attack can be serious. In particular, it becomes possible to decrypt data on a hard disk if it is possible to read the keys stored in RAM.

To detect the attack, Trammell used his own development – a hardware flash memory emulator spispy, which allows you to both track calls to the BIOS chip and replace the boot code on the fly, partially or in whole. The vulnerability is qualified as a Time-of-check / Time-of-Use (TOCTOU) error – this term describes a situation when the code is validated “at the wrong moment”, and after verification, the possibility of software substitution remains.

There is a hint in the study that hardware manufacturers often refuse additional validation of the BIOS code (Hudson discovered the problem in devices from five different vendors). Perhaps they are doing this because of the requirements of Microsoft, which imposes serious restrictions on the time the Windows logo appears after waking up from sleep. If that’s true, safety has been sacrificed for user comfort. The problem is aggravated by the fact that such parameters are set in hardware and cannot be changed by software.

Although Hudson does not know exactly how Intel solved the problem, most likely the vendor’s settings are now partially ignored, and the new firmware of the CSME module forcibly checks the validity of the BIOS code upon exiting sleep.
Attacks like the one described by Hudson, by definition, cannot be massive, but it will not be easy to close the vulnerability – you have to wait until the patch reaches specific devices through the laptop or motherboard manufacturer. On the other hand, you can protect valuable data from such an attack yourself: just turn off your laptop in situations where it is left unattended.

What else happened

Kaspersky Lab experts in detail considered the operation of two ransomware Trojans, Ragnar Locker and Egregor. These two examples show how cybercriminals not only extort money for decryption, but also steal victims’ data and threaten to publish it.

Nvidia closed another major bug in its software, this time in the GeForce Now software. The arbitrary code execution vulnerability is related to the open source library OpenSSL used in the software.

Avast found on Google Play, a bunch of applications that supposedly extend the functionality of the Minecraft game, but in fact charge the victims $ 30 a week.

Microsoft Monthly Patch Kit closed at least one Zero-Day (we wrote about this vulnerability two weeks ago), as well as a serious vulnerability in the Network File System service. Another vulnerability (CVE-2020-1599) allows malicious code to attach to an executable file, while maintaining the validity of the digital signature. Meanwhile, two more zero-days patched in the Google Chrome browser.

Apple requires from software suppliers to provide a manifest with a detailed description of how to work with user data. The company itself is being criticized (see tweet above) for new functionality in macOS Big Sur: system applications can now connect directly to the company’s servers, ignoring custom firewalls and VPN clients. First, this practice can be exploited by malware. Secondly, this approach reveals the real IP of the user, even if he wants to hide it.

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