CVE-2020-3957 in Fusion
Summary
by MITRE
VMware Fusion (11.x before 11.5.5), VMware Remote Console for Mac (11.x and prior) and VMware Horizon Client for Mac (5.x and prior) contain a local privilege escalation vulnerability due to a Time-of-check Time-of-use (TOCTOU) issue in the service opener. Successful exploitation of this issue may allow attackers with normal user privileges to escalate their privileges to root on the system where Fusion, VMRC and Horizon Client are installed.
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Analysis
by VulDB Data Team • 10/21/2020
This vulnerability exists in VMware Fusion versions 11.x before 11.5.5, VMware Remote Console for Mac versions 11.x and prior, and VMware Horizon Client for Mac versions 5.x and prior. The flaw stems from a time-of-check time-of-use vulnerability in the service opener component, which creates a window where an attacker can manipulate system state between the moment when a security check is performed and when the actual operation is executed. This specific TOCTOU issue falls under CWE-367, which addresses the dangerous use of time-of-check to time-of-use conditions that can lead to privilege escalation attacks. The vulnerability allows unprivileged users to potentially gain root access on affected systems, making it a critical security concern for macOS environments running these VMware products.
The technical implementation of this vulnerability involves the service opener functionality that manages the execution of privileged operations. When a normal user attempts to perform certain actions, the system performs a security check to determine if the operation should be permitted. However, due to the TOCTOU race condition, an attacker can modify the system state between the check and the actual execution of the operation. This manipulation can involve replacing executable files, modifying file permissions, or altering system configuration elements that the privileged process will subsequently use. The service opener component in these VMware applications fails to properly validate the integrity of the system state during the critical execution phase, allowing malicious actors to exploit this window of opportunity.
The operational impact of this vulnerability is significant as it enables local privilege escalation from standard user level to root privileges, which represents a complete compromise of system security. Attackers exploiting this vulnerability can gain unrestricted access to system resources, including the ability to install malicious software, modify system files, access sensitive data, and potentially establish persistence mechanisms. This vulnerability affects macOS environments where these VMware products are installed, making it particularly concerning for enterprise environments that rely on VMware virtualization solutions. The attack vector requires local system access, meaning an attacker must first have user-level access to the target system, but once exploited, the consequences are severe as the attacker can then perform any action with system-level privileges.
The exploitation of this vulnerability typically involves creating a race condition scenario where the attacker manipulates files or system state between the time the security check occurs and when the privileged operation executes. This can be achieved through various techniques including symbolic link manipulation, file replacement attacks, or process injection methods. The vulnerability affects multiple VMware products, indicating a systemic issue in how these applications handle privileged operations on macOS platforms. Organizations should immediately apply the vendor patches released for versions 11.5.5 and later for Fusion, and corresponding updates for Remote Console and Horizon Client products. Security monitoring should focus on detecting unusual file system modifications and privilege escalation attempts. Additionally, implementing least privilege principles and maintaining updated system configurations can help mitigate the risk of exploitation. This vulnerability also aligns with ATT&CK technique T1068 which covers local privilege escalation through race conditions and TOCTOU vulnerabilities, emphasizing the need for proper system state validation during critical operations.