Microsoft Windows: 'Download More RAM' Vulnerability Chain Bypasses VBS and HVCI

Researchers from the University of Birmingham and SeriSec have identified a critical vulnerability chain, dubbed "Download More RAM," that targets the Microsoft Windows kernel and hypervisor. The exploit leverages a sequence of three distinct vulnerabilities to circumvent Virtualization-Based Security (VBS) and Hypervisor-Protected Code Integrity (HVCI). By breaking the hardware-backed root of trust and undermining hypervisor-enforced memory isolation, attackers can achieve kernel-mode code integrity bypass. This allows for the execution of automated scripts designed to disable Microsoft Defender and other third-party Endpoint Detection and Response (EDR) solutions. The chain is reportedly delivered via the "PolitePaul" service, requiring minimal user interaction and enabling remote execution without physical access.

• Vulnerability Overview: The 'Download More RAM' Chain

  • Consists of a coordinated chain of three distinct Windows kernel and hypervisor vulnerabilities.
  • Specifically targets the isolation layers between the standard OS and secure memory regions.
  • Aims to degrade the system's hardware-backed security posture to a software-only state.

• Technical Mechanics: Bypassing VBS and HVCI

  • Circumvents Virtualization-Based Security (VBS) to compromise secure memory segmentation.
  • Breaks Hypervisor-Protected Code Integrity (HVCI), enabling the execution of unsigned or malicious kernel-mode code.
  • Successfully invalidates the hypervisor-enforced memory isolation intended to protect critical system processes.

• Exploitation and Delivery: The PolitePaul Service

  • Leverages the "PolitePaul" delivery mechanism to facilitate initial access.
  • Supports remote execution capabilities, removing the requirement for local or physical device access.
  • Features a low-interaction requirement, significantly lowering the barrier for successful exploitation.

• Impact Assessment: Endpoint Neutralization

  • Enables the deployment of automated scripts to instantaneously disable Microsoft Defender.
  • Provides a mechanism to neutralize third-party EDR and antivirus software at the kernel level.
  • Results in the complete loss of the operating system's hardware-enforced root of trust.

• Defense Implications: Systemic Risks

  • Demonstrates the fragility of software-defined security when the underlying hypervisor is compromised.
  • Highlights a critical need for enhanced kernel-mode integrity monitoring.
  • Necessitates urgent patching of the identified three-flaw chain to restore VBS/HVCI efficacy.