CVE-2019-15690 in Server
Summary
by MITRE • 01/24/2025
LibVNCServer 0.9.12 release and earlier contains heap buffer overflow vulnerability within the HandleCursorShape() function in libvncclient/cursor.c. An attacker sends cursor shapes with specially crafted dimensions, which can result in remote code execution.
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Analysis
by VulDB Data Team • 01/24/2025
The vulnerability identified as CVE-2019-15690 represents a critical heap buffer overflow flaw within LibVNCServer version 0.9.12 and earlier releases. This issue resides in the HandleCursorShape() function located in the libvncclient/cursor.c file, making it a core component of the remote desktop protocol implementation that governs cursor handling within VNC connections. The flaw manifests when the software processes cursor shape data transmitted over network connections, creating an exploitable condition that can be leveraged by remote attackers to execute arbitrary code on affected systems.
The technical implementation of this vulnerability stems from inadequate bounds checking during the processing of cursor shape dimensions. When an attacker crafts malicious cursor shape data with oversized or malformed dimensions, the application fails to properly validate these parameters before attempting to allocate memory for cursor rendering operations. This deficiency allows the software to write beyond the allocated heap buffer boundaries, potentially overwriting adjacent memory regions with attacker-controlled data. The vulnerability operates at the intersection of memory safety and network protocol handling, where network-transmitted data directly influences memory allocation decisions without proper sanitization.
From an operational impact perspective, this vulnerability presents a severe threat to systems utilizing LibVNCServer for remote desktop functionality. Attackers can exploit this flaw remotely without authentication requirements, making it particularly dangerous in environments where VNC servers are exposed to untrusted networks or the internet. Successful exploitation can result in complete system compromise, allowing attackers to execute arbitrary code with the privileges of the affected service. The vulnerability affects a wide range of applications that depend on LibVNCServer, including remote desktop solutions, virtualization platforms, and network management tools that implement VNC protocols for remote access.
The security implications extend beyond immediate code execution capabilities to encompass potential privilege escalation and persistent access mechanisms. Attackers can leverage this vulnerability to gain unauthorized access to systems, potentially establishing backdoors or exfiltrating sensitive data. The vulnerability aligns with CWE-121, heap-based buffer overflow, and maps to ATT&CK technique T1059 for command and script injection, while also supporting T1071 for application layer protocol usage. Organizations using vulnerable versions of LibVNCServer should prioritize immediate remediation through patching or implementing network segmentation controls to prevent unauthorized access to VNC services. The flaw demonstrates the critical importance of input validation in network protocols and highlights the need for robust memory safety practices in widely-deployed open source components that handle network-transmitted data.