CVE-2019-5518 in ESXi
Summary
by MITRE
VMware ESXi (6.7 before ESXi670-201903001, 6.5 before ESXi650-201903001, 6.0 before ESXi600-201903001), Workstation (15.x before 15.0.4, 14.x before 14.1.7), Fusion (11.x before 11.0.3, 10.x before 10.1.6) contain an out-of-bounds read/write vulnerability in the virtual USB 1.1 UHCI (Universal Host Controller Interface). Exploitation of this issue requires an attacker to have access to a virtual machine with a virtual USB controller present. This issue may allow a guest to execute code on the host.
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Analysis
by VulDB Data Team • 08/21/2023
The vulnerability identified as CVE-2019-5518 represents a critical out-of-bounds read/write flaw within the virtual USB 1.1 UHCI (Universal Host Controller Interface) implementation across multiple VMware products including ESXi, Workstation, and Fusion. This vulnerability resides in the hypervisor's USB controller emulation layer, specifically affecting versions prior to the mentioned security patches. The flaw manifests as a memory access violation that occurs when processing USB transfer requests through the Universal Host Controller Interface, which is responsible for managing USB 1.1 devices in virtualized environments. The vulnerability's presence in the UHCI controller implementation creates a potential pathway for privilege escalation from guest operating system level to host system level execution, as the underlying memory management does not properly validate bounds during USB data transfer operations.
The technical exploitation of this vulnerability requires an attacker to first gain access to a running virtual machine that has a virtual USB controller configured and active. This prerequisite significantly limits the attack surface but does not eliminate the risk, as many virtual environments include USB controller devices for various legitimate purposes including hardware device passthrough, storage device access, and peripheral connectivity. The out-of-bounds memory access occurs during USB transaction processing when the virtual UHCI controller fails to properly validate input parameters or buffer boundaries, allowing an attacker to manipulate memory locations beyond the intended buffer limits. This type of vulnerability maps directly to CWE-125 (Out-of-bounds Read) and CWE-787 (Out-of-bounds Write) categories, which are commonly exploited in hypervisor escape scenarios due to the privileged nature of virtualization layers.
The operational impact of this vulnerability extends beyond simple data corruption or system instability, as successful exploitation enables guest-to-host code execution capabilities that can fundamentally compromise the security isolation that virtualization platforms are designed to provide. An attacker who successfully exploits this vulnerability could potentially execute arbitrary code on the host system with the privileges of the hypervisor process, which typically runs with elevated system privileges. This scenario creates a complete breakdown of the virtualization security model, as the hypervisor's role is to maintain strict separation between guest operating systems and the underlying host system. The vulnerability's classification under ATT&CK technique T1055 (Process Injection) and T1072 (Software Deployment Tools) reflects the potential for privilege escalation and lateral movement within the compromised environment, as the attacker could leverage the host-level execution capabilities to further compromise the infrastructure.
Mitigation strategies for CVE-2019-5518 primarily focus on applying the vendor-provided security patches and updates that address the specific memory access validation issues within the USB controller implementation. Organizations should prioritize patching all affected VMware products including ESXi hosts, Workstation installations, and Fusion environments, with particular attention to systems that host sensitive workloads or operate in multi-tenant environments where guest isolation is critical. Additional defensive measures include disabling unnecessary USB controller devices in virtual machines, implementing network segmentation to limit potential attack vectors, and monitoring for unusual USB-related activity within virtual environments. Security teams should also consider implementing virtualization-specific monitoring solutions that can detect anomalous behavior patterns consistent with hypervisor escape attempts, as these vulnerabilities often manifest through subtle memory access patterns that may not be immediately obvious through traditional security monitoring approaches. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date virtualization infrastructure and the inherent security risks present in complex virtualization environments where multiple layers of abstraction create additional attack surfaces.