CVE-2020-3995 in ESXi
Summary
by MITRE • 10/21/2020
In VMware ESXi (6.7 before ESXi670-201908101-SG, 6.5 before ESXi650-202007101-SG), Workstation (15.x before 15.1.0), Fusion (11.x before 11.1.0), the VMCI host drivers used by VMware hypervisors contain a memory leak vulnerability. A malicious actor with access to a virtual machine may be able to trigger a memory leak issue resulting in memory resource exhaustion on the hypervisor if the attack is sustained for extended periods of time.
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Analysis
by VulDB Data Team • 11/22/2020
The vulnerability identified as CVE-2020-3995 represents a critical memory management flaw within VMware's virtualization infrastructure affecting multiple product lines including ESXi hypervisor versions and VMware Workstation and Fusion desktop virtualization products. This vulnerability resides in the VMCI (Virtual Machine Communication Interface) host drivers that facilitate communication between virtual machines and the underlying hypervisor. The memory leak occurs when malicious code executing within a compromised virtual machine repeatedly invokes VMCI driver functions without proper resource cleanup, leading to gradual consumption of available memory resources on the host system. The affected versions span across VMware ESXi 6.7 and 6.5 releases, as well as VMware Workstation 15.x and Fusion 11.x, indicating a widespread impact across VMware's virtualization portfolio. This vulnerability is particularly concerning because it leverages the inherent trust relationship between virtual machines and hypervisors, where a compromised guest operating system can exploit legitimate driver interfaces to perform resource exhaustion attacks.
The technical implementation of this vulnerability stems from inadequate memory management practices within the VMCI host driver components. When virtual machines make repeated calls to VMCI services, the driver fails to properly release allocated memory structures, creating a gradual accumulation of unreleased memory blocks. This memory leak manifests as a steady degradation of available system memory on the hypervisor host, potentially leading to system instability, performance degradation, or complete system crashes. The vulnerability's exploitation requires a malicious actor to have compromised access to a virtual machine and to maintain sustained execution within that environment. The attack vector is particularly insidious because it operates within the legitimate communication channels established by VMware's virtualization framework, making it difficult to detect through conventional security monitoring approaches. The memory exhaustion typically occurs over extended periods, suggesting that the attack may be designed to remain persistent and undetected while gradually consuming system resources.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on VMware virtualization environments, particularly in cloud computing and data center deployments where resource efficiency is critical. The memory leak can lead to cascading failures where legitimate virtual machines begin experiencing performance degradation or resource allocation issues as host memory becomes increasingly constrained. In large-scale deployments, this could result in service disruption across multiple virtual machines hosted on the same physical system. The vulnerability also increases the attack surface for lateral movement within virtualized environments, as compromised virtual machines can potentially exhaust resources on the hypervisor, affecting other tenants in multi-tenant cloud deployments. Organizations with limited memory resources or those operating under strict resource constraints face the highest risk from this vulnerability, as even moderate memory consumption can quickly lead to system instability.
Mitigation strategies for CVE-2020-3995 require immediate implementation of VMware's official security patches and updates for all affected versions. Organizations should prioritize patching their ESXi hypervisor installations, particularly focusing on the specific build numbers mentioned in the vulnerability advisory. System administrators should implement monitoring solutions that track memory usage patterns on hypervisor hosts to detect unusual consumption trends that may indicate exploitation attempts. Network segmentation and access controls should be strengthened to limit potential attack vectors into virtual machines, reducing the likelihood of compromise. The vulnerability aligns with CWE-401 Memory Leak, which specifically addresses insufficient resource deallocation, and represents a potential technique for maintaining persistence through resource exhaustion as outlined in MITRE ATT&CK technique T1499.1 for Resource Hijacking. Regular security assessments of virtualization environments should include verification of patch status and memory management configurations to ensure continued protection against this and similar vulnerabilities. Organizations should also consider implementing automated patch management solutions to maintain up-to-date security posture across their virtualized infrastructure.