CVE-2001-0168 in WinVNC
Summary
by MITRE
Buffer overflow in AT&T WinVNC (Virtual Network Computing) server 3.3.3r7 and earlier allows remote attackers to execute arbitrary commands via a long HTTP GET request when the DebugLevel registry key is greater than 0.
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Analysis
by VulDB Data Team • 05/25/2025
The vulnerability identified as CVE-2001-0168 represents a critical buffer overflow flaw within AT&T WinVNC server versions 3.3.3r7 and earlier. This security weakness specifically manifests when the DebugLevel registry key is configured to a value greater than zero, creating a condition where remote attackers can exploit the software's handling of HTTP GET requests. The vulnerability stems from inadequate input validation and memory management practices within the VNC server implementation, allowing malicious actors to craft overly long HTTP requests that exceed the allocated buffer space. Such buffer overflows typically occur when programs fail to properly check the length of incoming data before copying it into fixed-size memory buffers, leading to memory corruption that can be leveraged for arbitrary code execution.
The technical exploitation of this vulnerability requires remote access to the affected VNC server and the ability to send specially crafted HTTP GET requests through the network interface. When the DebugLevel registry key exceeds zero, the server's logging mechanism becomes more verbose and susceptible to memory corruption during HTTP request processing. The buffer overflow occurs in the HTTP request parsing component where the server fails to validate the length of the requested URI or parameters before copying them into internal buffers. This flaw falls under the Common Weakness Enumeration category of CWE-121, which describes stack-based buffer overflow conditions, and also relates to CWE-787, representing out-of-bounds write vulnerabilities. The attack vector is classified as remote network-based, making it particularly dangerous as it requires no local access to the target system and can be exploited from anywhere on the internet.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with the capability to execute arbitrary commands on the compromised system with the privileges of the VNC server process. This elevated privilege execution can lead to complete system compromise, allowing attackers to install backdoors, exfiltrate sensitive data, or establish persistent access to the network. The vulnerability affects organizations using older versions of WinVNC software, particularly those in enterprise environments where remote desktop access is common. Security practitioners should note that this vulnerability was particularly concerning in the early 2000s when remote desktop protocols were becoming increasingly prevalent in business environments. The attack can be automated and does not require sophisticated techniques, making it attractive to script kiddies and automated exploitation tools. Organizations that failed to patch this vulnerability were at significant risk of unauthorized access to their systems, potentially leading to data breaches, system compromise, and regulatory compliance violations.
Mitigation strategies for CVE-2001-0168 primarily involve immediate software updates to versions that address the buffer overflow vulnerability, as well as configuration hardening to prevent exploitation. System administrators should disable the DebugLevel registry key or set it to zero to prevent the vulnerable code path from being executed. Additionally, network-level firewalls should be configured to restrict access to VNC ports to trusted networks only, and intrusion detection systems should be deployed to monitor for suspicious HTTP GET requests. The vulnerability also highlights the importance of secure coding practices and input validation, as outlined in the ATT&CK framework under techniques related to command and control communications. Organizations should implement regular vulnerability assessments and penetration testing to identify similar buffer overflow vulnerabilities in other network services and applications. The remediation process should include thorough testing of patched software to ensure that the fix does not introduce new issues while maintaining the availability of legitimate remote access services.