CVE-2018-7226 in LinuxVNC
Summary
by MITRE
An issue was discovered in vcSetXCutTextProc() in VNConsole.c in LinuxVNC and VNCommand from the LibVNC/vncterm distribution through 0.9.10. Missing sanitization of the client-specified message length may cause integer overflow or possibly have unspecified other impact via a specially crafted VNC packet.
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Analysis
by VulDB Data Team • 09/08/2025
The vulnerability identified as CVE-2018-7226 represents a critical integer overflow flaw within the LinuxVNC and VNCommand implementations that affects versions through 0.9.10. This issue resides in the vcSetXCutTextProc() function located in the VNConsole.c file of the LibVNC/vncterm distribution, exposing systems to potential exploitation through malformed VNC protocol communications. The vulnerability stems from inadequate input validation mechanisms that fail to properly sanitize client-specified message lengths, creating a pathway for malicious actors to manipulate protocol parsing behaviors.
The technical implementation of this vulnerability demonstrates a classic integer overflow condition where an attacker can craft specially designed VNC packets containing malformed length fields that, when processed by the vulnerable function, result in arithmetic overflow conditions. This overflow can potentially lead to memory corruption, arbitrary code execution, or system instability. The flaw operates at the protocol level where client-supplied data directly influences memory allocation calculations, making it particularly dangerous in networked environments where untrusted clients can connect to VNC servers. The vulnerability falls under CWE-190, which specifically addresses integer overflow and underflow conditions, and can be categorized under ATT&CK technique T1059 for execution through command injection or memory corruption.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the integer overflow conditions can be leveraged to achieve more sophisticated exploitation techniques including memory corruption attacks and privilege escalation. Systems running vulnerable versions of LinuxVNC or VNCommand are at risk of being compromised when they accept connections from untrusted clients, making this particularly concerning for remote desktop services, virtual machine environments, and any infrastructure relying on VNC protocol for remote access. The vulnerability's exploitation potential increases when VNC servers are exposed to the internet or operate in less secure network environments where client authentication is minimal or absent.
Mitigation strategies for CVE-2018-7226 require immediate patching of affected systems to versions that properly sanitize client message lengths and implement robust input validation. Organizations should also consider network segmentation and access control measures to limit exposure of VNC services to untrusted networks. The implementation of proper bounds checking and integer overflow detection mechanisms within the vulnerable code paths provides the most effective long-term solution. Security monitoring should focus on detecting anomalous VNC packet structures and unusual memory allocation patterns that may indicate exploitation attempts. Additionally, system administrators should implement network-level controls to restrict VNC access to trusted IP ranges and consider implementing additional authentication layers beyond the basic VNC password mechanisms to reduce the attack surface.