CVE-2008-5001 in UltraVNC
Summary
by MITRE
Multiple stack-based buffer overflows in multiple functions in vncviewer/FileTransfer.cpp in vncviewer for UltraVNC 1.0.2 and 1.0.4 before 01252008, when in LISTENING mode or when using the DSM plugin, allow remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via unspecified parameters, a different issue than CVE-2008-0610.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/03/2021
The vulnerability identified as CVE-2008-5001 represents a critical stack-based buffer overflow issue affecting UltraVNC versions 1.0.2 and 1.0.4 prior to the 01252008 release. This flaw exists within the vncviewer component specifically in the FileTransfer.cpp file, which handles file transfer operations between remote desktop sessions. The vulnerability manifests when the vncviewer application operates in LISTENING mode or when utilizing the DSM plugin functionality, creating a dangerous attack surface that can be exploited by remote adversaries. The flaw is classified as a stack-based buffer overflow under CWE-121, which occurs when data is written beyond the bounds of a fixed-length stack buffer, potentially corrupting adjacent memory locations and leading to unpredictable application behavior.
The technical implementation of this vulnerability stems from inadequate input validation within multiple functions in the FileTransfer.cpp module. When the vncviewer processes file transfer requests in LISTENING mode or through DSM plugin operations, it fails to properly validate the size and content of incoming parameters, allowing attackers to craft malicious input that exceeds the allocated buffer space. This insufficient boundary checking creates an exploitable condition where an attacker can overwrite adjacent stack memory, potentially corrupting return addresses, function pointers, or other critical program state information. The vulnerability is particularly concerning because it can be triggered without authentication, making it accessible to any remote attacker who can establish a connection to the vulnerable vncviewer instance, and it specifically relates to the DSM (Data Security Module) plugin functionality which adds additional complexity to the attack surface.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable remote code execution, making it a severe security risk for systems utilizing vulnerable UltraVNC implementations. When exploited successfully, the buffer overflow can cause the vncviewer application to crash and terminate unexpectedly, resulting in service disruption for legitimate users. However, the more dangerous aspect involves the potential for arbitrary code execution, where an attacker could leverage the corrupted stack memory to inject and execute malicious code with the privileges of the vncviewer process. This could lead to complete system compromise, especially if the vncviewer is running with elevated privileges. The vulnerability affects systems where remote desktop functionality is exposed to untrusted networks, creating a significant risk for enterprise environments where such services might be improperly configured or secured.
The remediation approach for this vulnerability requires immediate patching of UltraVNC installations to versions released after 01252008, which contain the necessary fixes for the buffer overflow conditions. Organizations should also implement network segmentation to limit access to vncviewer services, particularly when operating in LISTENING mode, and consider disabling unnecessary plugin functionality such as the DSM plugin if not required for operations. Security monitoring should be enhanced to detect unusual connection patterns or malformed file transfer requests that might indicate exploitation attempts. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and T1071.004 (Application Layer Protocol: DNS) when considering the network-based attack vectors. Additionally, the vulnerability demonstrates the importance of proper input validation and memory safety practices, which should be reinforced through secure coding guidelines and regular security assessments. Organizations should also consider implementing network-based intrusion detection systems to monitor for potential exploitation attempts targeting this specific vulnerability, as the attack patterns are predictable and can be detected through signature-based monitoring.