CVE-2020-14401 in LibVNCServer
Summary
by MITRE
An issue was discovered in LibVNCServer before 0.9.13. libvncserver/scale.c has a pixel_value integer overflow.
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Analysis
by VulDB Data Team • 06/18/2020
The vulnerability identified as CVE-2020-14401 represents a critical integer overflow flaw within LibVNCServer version 0.9.12 and earlier, which is a widely used open-source library implementing the Virtual Network Computing protocol. This library facilitates remote desktop access and control across networked systems, making it a critical component in various enterprise and consumer environments. The flaw specifically resides in the libvncserver/scale.c file, where an integer overflow occurs during pixel value processing, potentially allowing attackers to manipulate memory operations through carefully crafted input data.
The technical implementation of this vulnerability stems from improper handling of integer arithmetic within the scaling functionality of the VNC server implementation. When processing scaled pixel data, the code performs calculations that can exceed the maximum representable value for a 32-bit signed integer, causing an overflow condition. This overflow can result in unexpected behavior where the calculated pixel values wrap around to negative numbers or other unintended values, potentially leading to memory corruption or arbitrary code execution. The vulnerability is particularly concerning because it occurs during the processing of graphical data, which is continuously transmitted during VNC sessions, making exploitation relatively straightforward for attackers who can influence the graphical content being processed.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it creates potential pathways for remote code execution and privilege escalation attacks. Attackers who can establish a connection to a vulnerable VNC server and influence the graphical content being transmitted may exploit this integer overflow to manipulate memory layout, potentially overwriting critical data structures or executing malicious code. This risk is exacerbated by the widespread deployment of LibVNCServer in various network environments including corporate networks, cloud infrastructures, and remote access solutions where VNC servers are commonly deployed for administrative purposes.
Mitigation strategies for CVE-2020-14401 primarily focus on immediate software updates to LibVNCServer version 0.9.13 or later, which contains the necessary patches to address the integer overflow condition. System administrators should prioritize patching all affected systems, particularly those running VNC servers in production environments where remote access capabilities are utilized. Additional defensive measures include implementing network segmentation to limit access to VNC servers, enforcing strong authentication mechanisms, and monitoring network traffic for suspicious graphical data patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and can be mapped to ATT&CK technique T1071.004 for application layer protocol usage in network communications. Organizations should also consider implementing intrusion detection systems capable of identifying anomalous VNC traffic patterns that could indicate exploitation attempts targeting this specific vulnerability.