CVE-2020-14404 in LibVNCServer
Summary
by MITRE
An issue was discovered in LibVNCServer before 0.9.13. libvncserver/rre.c allows out-of-bounds access via encodings.
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Analysis
by VulDB Data Team • 06/18/2020
The vulnerability identified as CVE-2020-14404 represents a critical out-of-bounds memory access flaw within LibVNCServer version 0.9.12 and earlier. This issue resides in the libvncserver/rre.c component which handles RRE (Raw Run-Length Encoding) data processing for VNC server implementations. The vulnerability manifests when the VNC server processes malformed encoding data, specifically in how it handles the RRE encoding format during remote desktop protocol communication. This flaw allows attackers to potentially execute arbitrary code or cause denial of service conditions through carefully crafted malicious VNC client connections.
The technical implementation of this vulnerability stems from insufficient input validation and boundary checking within the RRE decoding routine. When processing incoming VNC client data, the affected code fails to properly validate array indices or buffer boundaries before accessing memory locations. This type of flaw falls under CWE-129 Input Validation and Output Encoding, specifically manifesting as an out-of-bounds read condition. The vulnerability is particularly concerning because it can be exploited through network-based attacks without requiring authentication, making it accessible to remote attackers who can establish VNC connections to vulnerable servers. The RRE encoding format is commonly used in VNC implementations for efficient transmission of screen updates, which makes this flaw particularly dangerous as it can be triggered during normal VNC operation.
The operational impact of CVE-2020-14404 extends beyond simple denial of service scenarios to include potential remote code execution capabilities. Attackers who successfully exploit this vulnerability can cause the VNC server process to crash or potentially execute arbitrary code with the privileges of the VNC server process. This vulnerability affects various systems that rely on LibVNCServer for remote desktop functionality including virtual machine management platforms, remote access solutions, and enterprise desktop management systems. The attack surface is broad as any system running a vulnerable version of LibVNCServer and accepting VNC connections is at risk. Organizations using VNC servers for remote administration, kiosk applications, or virtual desktop infrastructure are particularly vulnerable to this type of attack vector.
Mitigation strategies for CVE-2020-14404 primarily involve upgrading to LibVNCServer version 0.9.13 or later where the vulnerability has been patched. System administrators should prioritize patching all affected VNC server implementations across their network infrastructure. Network segmentation and firewall rules can provide temporary protection by restricting VNC server access to trusted networks only. Additional protective measures include implementing intrusion detection systems to monitor for suspicious VNC traffic patterns and conducting regular vulnerability assessments of remote access infrastructure. From an ATT&CK framework perspective, this vulnerability maps to T1021.001 Remote Services and T1190 Exploit Public-Facing Application, as it represents an exploitation of publicly accessible VNC services. Organizations should also consider implementing network monitoring solutions that can detect anomalous VNC protocol behavior and establish baseline network traffic patterns to identify potential exploitation attempts.