CVE-2020-3958 in ESXi
Summary
by MITRE
VMware ESXi (6.7 before ESXi670-202004101-SG and 6.5 before ESXi650-202005401-SG), VMware Workstation (15.x before 15.5.2) and VMware Fusion (11.x before 11.5.2) contain a denial-of-service vulnerability in the shader functionality. Successful exploitation of this issue may allow attackers with non-administrative access to a virtual machine to crash the virtual machine's vmx process leading to a denial of service condition.
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Analysis
by VulDB Data Team • 10/21/2020
The vulnerability identified as CVE-2020-3958 represents a significant denial-of-service weakness affecting VMware's virtualization platforms including ESXi hypervisor versions 6.7 and 6.5, as well as VMware Workstation 15.x and Fusion 11.x. This flaw specifically targets the shader functionality within these virtual environments, creating a pathway for attackers to disrupt system operations without requiring administrative privileges. The vulnerability manifests when malicious actors exploit weaknesses in how these virtualization products handle graphics processing operations, particularly those involving shader computations that are essential for rendering visual content in virtual machines. The affected systems demonstrate a critical design flaw in their input validation and resource management mechanisms, allowing unauthorized users to manipulate shader-related processes and trigger system instability.
The technical exploitation of this vulnerability occurs through carefully crafted shader code or graphics operations that cause the virtual machine's vmx process to crash. This process represents the core virtual machine monitor component responsible for managing virtual machine execution and hardware abstraction. When the shader functionality encounters malformed or malicious input, it triggers an unhandled exception that propagates through the virtualization stack, ultimately leading to the termination of the vmx process. The vulnerability stems from insufficient bounds checking and memory management within the graphics processing subsystem, creating a condition where legitimate graphics operations can be manipulated to cause system-wide crashes. This type of flaw aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which addresses out-of-bounds read vulnerabilities that can lead to process termination.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates opportunities for attackers to leverage this weakness as part of broader attack strategies. In enterprise environments, where virtualization platforms serve as foundational infrastructure, a successful exploitation could lead to widespread service degradation affecting multiple virtual machines simultaneously. The vulnerability particularly concerns organizations using these virtualization products for development, testing, or production workloads, as it could be exploited to disrupt critical business operations. From an adversary perspective, this vulnerability provides a low-effort, high-impact method for causing service disruption, making it attractive for both malicious actors seeking to cause damage and for attackers conducting reconnaissance activities. The vulnerability's classification under ATT&CK technique T1499.004, which covers network denial of service, highlights its potential for causing operational disruption.
Mitigation strategies for CVE-2020-3958 primarily focus on applying the vendor-provided patches and updates that address the specific shader processing vulnerabilities. VMware has released updates for all affected versions, including ESXi patches for versions 6.7 and 6.5, and updated releases for Workstation 15.5.2 and Fusion 11.5.2. Organizations should prioritize immediate deployment of these patches across their virtualization infrastructure, particularly in environments where multiple users have access to virtual machines. Additional protective measures include implementing network segmentation to limit access to virtualization management interfaces, monitoring for unusual graphics processing patterns, and establishing robust incident response procedures for handling potential exploitation attempts. Security teams should also consider implementing virtual machine isolation measures and restricting user privileges within virtual environments to minimize the potential impact of successful exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date virtualization software and highlights the critical need for continuous security monitoring in virtualized environments where graphics processing capabilities are exposed to potentially untrusted users.