CVE-2017-4933 in ESXi
Summary
by MITRE
VMware ESXi (6.5 before ESXi650-201710401-BG), Workstation (12.x before 12.5.8), and Fusion (8.x before 8.5.9) contain a vulnerability that could allow an authenticated VNC session to cause a heap overflow via a specific set of VNC packets resulting in heap corruption. Successful exploitation of this issue could result in remote code execution in a virtual machine via the authenticated VNC session. Note: In order for exploitation to be possible in ESXi, VNC must be manually enabled in a virtual machine's .vmx configuration file. In addition, ESXi must be configured to allow VNC traffic through the built-in firewall.
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Analysis
by VulDB Data Team • 01/18/2023
This vulnerability exists within VMware's virtualization platforms including ESXi, Workstation, and Fusion where an authenticated VNC session can trigger a heap overflow condition through specially crafted VNC packets. The flaw manifests as heap corruption that can potentially lead to remote code execution within the targeted virtual machine environment. The vulnerability specifically affects versions prior to the mentioned patches where ESXi requires manual VNC configuration in the .vmx file and firewall rule configuration to enable the attack vector. This represents a significant security risk as it allows authenticated attackers to escalate privileges and execute arbitrary code within virtual machine contexts. The heap overflow occurs during the processing of VNC packets, where insufficient input validation leads to memory corruption that can be exploited to gain unauthorized access to virtualized environments. The vulnerability is particularly concerning because it leverages legitimate VNC functionality that may be enabled in production environments, making it a potential target for sophisticated attacks.
The technical implementation of this vulnerability stems from inadequate memory management within the VNC protocol handling code. When VNC packets are processed, the system fails to properly validate packet lengths and content boundaries, allowing attackers to craft malicious packets that exceed allocated heap buffer sizes. This type of heap-based buffer overflow falls under the CWE-121 category of stack-based buffer overflow, though the specific implementation in this case affects heap memory structures. The vulnerability demonstrates poor input validation practices where the VNC packet processing code does not adequately check for buffer overflows before copying data into heap allocated memory regions. The authentication requirement means that attackers must first establish a valid VNC session, but once authenticated, they can leverage this vulnerability to escalate their privileges within the virtual machine environment.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially compromise entire virtualized infrastructures. When exploited successfully, the heap corruption can allow attackers to execute arbitrary code with the privileges of the virtual machine process, potentially leading to complete system compromise. This vulnerability particularly affects enterprise environments where virtualization is extensively used, as it provides a pathway for attackers to move laterally within virtualized networks. The requirement for manual VNC configuration in ESXi adds a layer of complexity to exploitation but also means that organizations with proper security configurations may be protected. However, the widespread use of VMware products means that many organizations may have VNC enabled without proper security monitoring, creating potential attack surfaces. The vulnerability also impacts both Workstation and Fusion products, indicating it affects both server and desktop virtualization environments, broadening the potential attack surface.
Organizations should implement immediate mitigations including updating to patched versions of VMware products, disabling VNC functionality where not required, and configuring proper firewall rules to restrict VNC traffic. Network segmentation and monitoring should be enhanced to detect unusual VNC activity patterns. The vulnerability highlights the importance of proper input validation and memory management in virtualization platforms. Security teams should conduct comprehensive assessments of their virtualized environments to identify any systems with VNC enabled and ensure proper patch management procedures are in place. Additionally, implementing network-based intrusion detection systems can help identify exploitation attempts of this vulnerability. The ATT&CK framework categorizes this as a privilege escalation technique through exploitation of software vulnerabilities, specifically targeting virtualization environments. Organizations should also consider implementing zero-trust network architectures that minimize the attack surface of virtualized environments and reduce the impact of potential exploitation. Regular security assessments and vulnerability scanning should include checks for improperly configured virtualization platforms to prevent unauthorized VNC access.