CVE-2017-4912 in Workstation
Summary
by MITRE
VMware Workstation (12.x prior to 12.5.3) and Horizon View Client (4.x prior to 4.4.0) contain multiple out-of-bounds read vulnerabilities in TrueType Font (TTF) parser in the TPView.dll. On Workstation, this may allow a guest to execute code or perform a Denial of Service on the Windows OS that runs Workstation. In the case of a Horizon View Client, this may allow a View desktop to execute code or perform a Denial of Service on the Windows OS that runs the Horizon View Client. Exploitation is only possible if virtual printing has been enabled. This feature is not enabled by default on Workstation but it is enabled by default on Horizon View.
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Analysis
by VulDB Data Team • 12/26/2020
The vulnerability identified as CVE-2017-4912 represents a critical out-of-bounds read flaw within the TrueType Font parsing functionality of VMware Workstation and Horizon View Client applications. This vulnerability specifically affects TPView.dll components in versions prior to the specified patches, creating a significant security risk for users running these virtualization products. The flaw exists in the TTF parser implementation where insufficient bounds checking allows maliciously crafted font data to trigger memory access violations that can be exploited for code execution or denial of service attacks.
The technical implementation of this vulnerability stems from inadequate input validation within the TrueType Font processing engine. When the TPView.dll component processes font files, it fails to properly validate the boundaries of font data structures, particularly in how it handles font table offsets and data lengths. This allows an attacker to craft specially formatted TTF files that, when processed by the vulnerable applications, cause the parser to read memory locations beyond the intended data boundaries. Such out-of-bounds reads can result in unpredictable behavior including memory corruption that may be leveraged for arbitrary code execution, or simply cause application crashes leading to denial of service conditions.
The operational impact of this vulnerability varies significantly based on the specific VMware product and configuration. In VMware Workstation environments, exploitation requires that virtual printing functionality be explicitly enabled, which is not the default setting, thereby reducing the attack surface. However, in Horizon View Client deployments, virtual printing is enabled by default, making this vulnerability more readily exploitable in enterprise environments. The guest operating system in Workstation scenarios can potentially execute code on the host Windows OS, while Horizon View Client vulnerabilities can enable code execution directly on the Windows desktop environment running the client application. Both scenarios represent significant privilege escalation risks that could allow attackers to compromise entire virtual desktop environments.
The exploitation of this vulnerability aligns with several ATT&CK techniques including privilege escalation through code injection and defense evasion via denial of service attacks. From a CWE perspective, this vulnerability maps to CWE-125: Out-of-bounds Read, which is a well-documented weakness in software applications that process structured data formats. The vulnerability also demonstrates characteristics of CWE-707: Improper Neutralization of Input During Web Page Generation, as the font processing functionality fails to properly sanitize input data before processing. Organizations utilizing VMware virtualization platforms should immediately implement patch management procedures to address this vulnerability, particularly in Horizon View environments where the default configuration exposes systems to attack. The recommended mitigation involves updating to VMware Workstation 12.5.3 or later and Horizon View Client 4.4.0 or later, while also reviewing and disabling virtual printing functionality where it is not required for business operations.