CVE-2007-2526 in VNC Manager
Summary
by MITRE
Heap-based buffer overflow in the ConnectAsyncEx function in VNC Viewer ActiveX control (scvncctrl.dll) in the SmartCode VNC Manager 3.6 allows remote attackers to execute arbitrary code via a long argument.
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Analysis
by VulDB Data Team • 09/12/2024
The vulnerability identified as CVE-2007-2526 represents a critical heap-based buffer overflow flaw within the SmartCode VNC Manager 3.6 software suite, specifically affecting the ConnectAsyncEx function of the VNC Viewer ActiveX control component known as scvncctrl.dll. This vulnerability exists within the context of remote desktop protocol implementations and exposes a fundamental security weakness in how input parameters are validated and handled when establishing VNC connections through the ActiveX interface. The flaw manifests when the ConnectAsyncEx function processes a long argument parameter, leading to memory corruption that can be exploited by remote attackers to execute arbitrary code on affected systems. The vulnerability's classification as heap-based indicates that the overflow occurs within dynamically allocated memory regions, making it particularly dangerous as it can overwrite adjacent memory structures and potentially corrupt program execution flow.
The technical implementation of this vulnerability stems from insufficient bounds checking within the ConnectAsyncEx function, which fails to validate the length of input arguments before copying them into fixed-size memory buffers. When a maliciously crafted argument exceeding the allocated buffer size is passed to this function, the excess data overflows into adjacent heap memory locations, potentially corrupting heap metadata or overwrite return addresses and function pointers. This type of vulnerability directly maps to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite heap data structures. The ActiveX control architecture further amplifies the risk as it operates within web browsers and other applications that trust ActiveX components, creating an attack surface that can be exploited through web-based delivery mechanisms without requiring local system access.
The operational impact of this vulnerability extends beyond simple code execution, as it enables remote attackers to gain complete control over systems running vulnerable versions of SmartCode VNC Manager. The exploitation scenario typically involves an attacker constructing a malicious web page or VNC connection string that triggers the vulnerable ConnectAsyncEx function with an oversized argument, resulting in arbitrary code execution with the privileges of the user running the vulnerable VNC Viewer component. This vulnerability is particularly concerning in enterprise environments where VNC viewers are commonly deployed for remote system administration, as it could allow attackers to establish persistent access to critical infrastructure. The attack vector is particularly effective because ActiveX controls are often automatically executed by web browsers without user confirmation, making exploitation possible through simple web page visits or email attachments containing malicious VNC connection parameters.
Mitigation strategies for CVE-2007-2526 must address both immediate remediation and long-term architectural security improvements. The primary recommendation involves updating to a patched version of SmartCode VNC Manager that resolves the buffer overflow condition through proper input validation and bounds checking mechanisms. Organizations should also implement network segmentation and access controls to limit exposure of VNC services to untrusted networks, while disabling ActiveX controls in web browsers when they are not specifically required for legitimate business operations. Security administrators should consider implementing application whitelisting policies that restrict execution of known vulnerable ActiveX controls, and deploy intrusion detection systems that can identify suspicious VNC connection patterns or malformed argument sequences. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving remote code execution through vulnerable software components and privilege escalation through exploitation of ActiveX controls, making it a significant concern for organizations implementing comprehensive threat hunting and incident response procedures. The vulnerability also highlights the importance of secure coding practices, particularly around input validation and memory management, which should be enforced through automated code review processes and security testing protocols.