CVE-2007-0756 in Chicken of the VNC
Summary
by MITRE
Chicken of the VNC (cotv) 2.0 allows remote attackers to cause a denial of service (application crash) via a large computer-name size value in a ServerInit packet, which triggers a failed malloc and a resulting NULL dereference.
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Analysis
by VulDB Data Team • 08/21/2024
The vulnerability identified as CVE-2007-0756 affects Chicken of the VNC version 2.0, a popular VNC client application for mac os x systems. This issue represents a classic buffer overflow condition that manifests through improper input validation during network protocol handling. The flaw specifically occurs when processing the ServerInit packet, which is part of the standard vnc protocol used for establishing remote desktop connections. The vulnerability stems from the application's failure to properly validate the size parameter of computer names transmitted during the initial connection phase, creating an exploitable condition that can be leveraged by remote attackers to disrupt service availability.
The technical mechanism behind this vulnerability involves a malformed ServerInit packet containing an excessively large computer-name size value that exceeds the application's expected buffer boundaries. When the cotv application processes this packet, it attempts to allocate memory using malloc with the oversized size value provided in the packet. This allocation fails due to the unreasonable size parameter, resulting in a NULL pointer return from malloc. The application then proceeds to dereference this NULL pointer during subsequent processing, leading to an application crash and subsequent denial of service condition. This represents a fundamental memory management error where the software does not properly handle allocation failures or validate input parameters before processing.
From an operational impact perspective, this vulnerability enables remote attackers to effectively perform denial of service attacks against systems running Chicken of the VNC 2.0 without requiring any authentication or privileged access. The attack can be executed from anywhere on the network, making it particularly dangerous in environments where vnc services are exposed to untrusted networks. The resulting application crash not only disrupts legitimate user sessions but also potentially leaves the system in an unstable state where further connections may be impossible until the application is manually restarted. This vulnerability directly impacts the availability aspect of the security triad by compromising the service's ability to maintain operational continuity.
The vulnerability maps to CWE-122, which describes "Heap-based Buffer Overflow" and aligns with ATT&CK technique T1499.1, specifically "Network Denial of Service" where adversaries leverage application-level vulnerabilities to disrupt service availability. Mitigation strategies should include immediate patching of the application to version 2.1 or later, which contains the necessary input validation fixes. Network segmentation and firewall rules should be implemented to restrict access to vnc services to trusted networks only, while also monitoring for unusual packet patterns that might indicate exploitation attempts. Additionally, implementing proper input validation at the network level and configuring applications to handle memory allocation failures gracefully would provide additional defense in depth measures against similar vulnerabilities in other software components.
This vulnerability demonstrates the critical importance of proper input validation and memory management practices in network applications, particularly those handling untrusted data from remote sources. The flaw serves as a reminder that even seemingly benign protocol elements like computer name fields can become attack vectors when proper validation mechanisms are absent. Organizations should implement comprehensive security testing procedures including fuzzing and input validation reviews to identify similar conditions in their software portfolios, as the consequences of such vulnerabilities extend beyond simple service disruption to potentially compromise broader system availability and user productivity.