CVE-2020-14400 in LibVNCServer
Summary
by MITRE
An issue was discovered in LibVNCServer before 0.9.13. Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c.
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Analysis
by VulDB Data Team • 08/04/2024
The vulnerability identified as CVE-2020-14400 resides within LibVNCServer version 0.9.13 and earlier, representing a critical memory access issue that exposes the software to potential exploitation through improper data alignment handling. This flaw specifically affects the translate.c component of the library, which is responsible for handling data translation operations during remote desktop sessions. The root cause stems from the improper handling of byte-aligned data when accessed through uint16_t pointers, creating a scenario where memory access patterns do not align with the expected data structure boundaries.
The technical implementation of this vulnerability manifests when the software processes incoming data streams through the VNC protocol implementation, particularly in scenarios involving pixel format conversions and data translation operations. The uint16_t pointer usage creates a mismatch between the actual memory alignment of the data and the expectations of the pointer dereferencing operations. This misalignment can lead to memory access violations or data corruption when the software attempts to read or write data that does not conform to the expected 16-bit aligned boundaries. The issue typically occurs during image processing or screen update operations where the VNC server translates pixel data from one format to another, creating opportunities for attackers to manipulate memory access patterns through crafted input data.
From an operational perspective, this vulnerability presents significant security implications for systems utilizing LibVNCServer for remote desktop functionality, particularly in enterprise environments where VNC servers are deployed for remote administration or support operations. Attackers could potentially exploit this weakness to execute arbitrary code on affected systems, leading to complete compromise of the remote desktop server and potentially broader network access. The vulnerability's impact extends beyond simple memory corruption as it can enable privilege escalation attacks, denial of service conditions, or information disclosure scenarios. The flaw is particularly concerning because it operates at the core translation layer of the VNC protocol implementation, making it a critical attack surface for adversaries targeting remote desktop infrastructure.
The vulnerability maps directly to CWE-121 Stack-based Buffer Overflow and CWE-125 Out-of-bounds Read categories within the Common Weakness Enumeration framework, as the improper memory access patterns can lead to buffer overflows or out-of-bounds memory reads. Additionally, this issue aligns with ATT&CK technique T1059 Command and Scripting Interpreter, as successful exploitation could enable adversaries to execute malicious code on compromised systems. The attack surface is further expanded through the use of techniques such as T1071.004 Application Layer Protocol: SSH and T1105 Remote File Copy, as attackers might leverage compromised VNC servers to establish persistent access or move laterally within networks. Organizations using vulnerable versions of LibVNCServer should implement immediate mitigations including version updates to 0.9.13 or later, network segmentation of VNC services, and deployment of intrusion detection systems to monitor for exploitation attempts.
Mitigation strategies should prioritize the immediate upgrade to LibVNCServer version 0.9.13 or higher, which contains the necessary patches addressing the byte alignment issues in the translate.c module. Network administrators should also implement firewall rules to restrict access to VNC services, limiting exposure to trusted networks only, and consider deploying additional security controls such as VPNs or bastion hosts for remote access. The implementation of memory safety controls and address space layout randomization should be considered as additional defensive measures. Regular security assessments of VNC implementations and monitoring for anomalous network traffic patterns related to VNC protocol usage will help detect potential exploitation attempts. Organizations should also maintain updated vulnerability management processes to ensure rapid deployment of security patches across all systems utilizing vulnerable software components.