CVE-2019-5519 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 a Time-of-check Time-of-use (TOCTOU) 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-2019-5519 represents a critical Time-of-check Time-of-use (TOCTOU) flaw within VMware's virtual USB 1.1 UHCI implementation across multiple product lines including ESXi hypervisor versions and VMware Workstation and Fusion desktop virtualization platforms. This vulnerability resides in the virtual USB controller's handling of device access permissions, creating a window where an attacker can manipulate the state between a permission check and actual device usage. The flaw specifically affects VMware ESXi versions 6.7, 6.5, and 6.0, as well as Workstation versions 15.x and 14.x, and Fusion versions 11.x and 10.x, all before their respective security patches released in March 2019. The vulnerability is categorized under CWE-367 which specifically addresses Time-of-Check to Time-of-Use flaws, making it a well-documented class of security weaknesses that can lead to privilege escalation and arbitrary code execution.
The technical exploitation of this vulnerability requires an attacker to already have access to a compromised virtual machine that contains a virtual USB controller. This prerequisite significantly reduces the attack surface but does not eliminate the risk entirely, as the vulnerability can be leveraged by malicious actors who have already achieved initial access to a guest operating system. The TOCTOU condition occurs when the virtual USB controller performs a permission check to determine if a guest operating system can access a particular USB device, but between that check and the actual device access operation, an attacker can manipulate the system state to bypass the security controls. This manipulation allows the guest to execute arbitrary code on the host system, effectively breaking the isolation that virtualization is designed to provide. The vulnerability is particularly dangerous because it can be exploited to gain host-level privileges from within a guest environment, potentially allowing attackers to compromise the entire virtualization infrastructure.
The operational impact of CVE-2019-5519 extends beyond individual virtual machines, as successful exploitation can lead to complete compromise of the host system and potentially affect other virtual machines running on the same host. This vulnerability directly violates the fundamental security principle of virtualization isolation, where guest operating systems should not be able to execute code on the host system. The attack vector represents a privilege escalation vulnerability that can be particularly devastating in multi-tenant environments such as cloud computing platforms, data centers, or enterprise virtualized infrastructures where multiple organizations' workloads share the same physical hardware. The vulnerability's potential for lateral movement within a virtualized environment makes it particularly attractive to attackers who seek to establish persistent access to critical infrastructure. This weakness can be mapped to ATT&CK technique T1059.007 for command and scripting interpreter, and T1078 for valid accounts, as successful exploitation would likely involve using compromised guest access to gain host-level privileges.
Mitigation strategies for CVE-2019-5519 should prioritize immediate patching of affected VMware products to the latest security releases, which include the March 2019 patches that address the TOCTOU vulnerability in the virtual USB controller implementation. Organizations should also implement network segmentation and access controls to limit guest VM access to physical USB devices when such access is not strictly required for business operations. Security teams should monitor for suspicious VM activity and consider disabling virtual USB controllers on systems where they are not essential for operations. The vulnerability highlights the importance of regular security updates and patch management processes, as well as the need for comprehensive security testing of virtualization components. Additional defensive measures include implementing host-based intrusion detection systems and monitoring for unauthorized code execution on virtualization hosts, as well as conducting regular security assessments of virtualized environments to identify similar vulnerabilities in other hypervisor components.