CVE-2019-8274 in UltraVNC
Summary
by MITRE
UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer offer handler, which can potentially in result code execution. This attack appears to be exploitable via network connectivity. This vulnerability has been fixed in revision 1212.
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Analysis
by VulDB Data Team • 07/31/2023
The vulnerability identified as CVE-2019-8274 represents a critical heap buffer overflow flaw within the UltraVNC remote desktop software version 1211. This issue specifically resides in the VNC server code component that handles file transfer offers, making it particularly dangerous for remote desktop environments where file operations are frequently conducted. The vulnerability affects the core functionality of UltraVNC's file transfer mechanism, which is integral to the remote desktop experience and allows users to transfer files between local and remote systems. The flaw exists in the server-side implementation that processes incoming file transfer requests from connected clients, creating a potential attack surface that could be exploited by malicious actors with network access to the vulnerable system.
The technical nature of this vulnerability stems from improper bounds checking within the file transfer offer handler code segment. When processing file transfer requests, the software fails to adequately validate the size or length of incoming data structures, allowing an attacker to provide maliciously crafted input that exceeds the allocated buffer space. This heap overflow condition occurs during the handling of file transfer offers, where the application attempts to copy user-supplied data into a fixed-size buffer without sufficient validation. The vulnerability is classified as a heap-based buffer overflow under CWE-121, which represents a common and severe class of memory corruption vulnerabilities that can lead to arbitrary code execution. The flaw demonstrates characteristics consistent with CWE-787, which describes out-of-bounds write operations that can overwrite adjacent memory locations, potentially corrupting program execution flow.
The operational impact of CVE-2019-8274 extends beyond simple denial of service scenarios, as it presents a direct path to remote code execution capabilities for attackers. This vulnerability can be exploited through network connectivity alone, requiring no local system access or authentication, making it particularly dangerous in enterprise environments where remote desktop services are commonly exposed to external networks. The attack vector leverages the inherent trust model of remote desktop protocols, where legitimate file transfer operations can be weaponized to deliver malicious payloads. Once exploited, the vulnerability could allow an attacker to execute arbitrary code with the privileges of the VNC server process, potentially leading to complete system compromise. The attack surface is particularly concerning given that UltraVNC is widely deployed in both corporate and personal environments, with the vulnerability affecting systems where remote desktop access is enabled for legitimate business operations.
Security professionals should consider this vulnerability in the context of the MITRE ATT&CK framework, particularly under the T1059 technique for command and control through remote services, and T1071 for application layer protocols. The vulnerability enables lateral movement and privilege escalation within networks where UltraVNC is deployed, as successful exploitation can provide attackers with persistent access to compromised systems. Organizations should prioritize immediate remediation by upgrading to UltraVNC revision 1212 or later, which contains the necessary patches to address the heap buffer overflow. Additional mitigations should include network segmentation to limit access to VNC services, implementation of strong authentication mechanisms, and monitoring for anomalous file transfer activities. The vulnerability highlights the importance of regular software updates and proper input validation in remote desktop applications, as these systems often become targets for sophisticated attacks due to their privileged access capabilities and the potential for remote code execution.