CVE-2019-15693 in TigerVNC
Summary
by MITRE • 01/25/2023
TigerVNC version prior to 1.10.1 is vulnerable to heap buffer overflow, which occurs in TightDecoder::FilterGradient. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 03/17/2024
The vulnerability identified as CVE-2019-15693 affects TigerVNC versions prior to 1.10.1 and represents a critical heap buffer overflow condition within the TightDecoder::FilterGradient component of the VNC server implementation. This flaw exists in the handling of compressed image data during the Tight encoding process, where insufficient bounds checking allows an attacker to write beyond allocated memory boundaries. The vulnerability is particularly concerning as it enables remote code execution when exploited through network connectivity, making it a significant threat to VNC server deployments across various network environments.
The technical root cause of this vulnerability stems from inadequate input validation within the TightDecoder::FilterGradient function, which processes gradient filtering operations for image compression. When processing maliciously crafted VNC client data, the function fails to properly validate the size of incoming data buffers before performing memory operations. This allows an attacker to craft specific VNC protocol messages that trigger a heap-based buffer overflow condition, potentially leading to arbitrary code execution on the target system. The vulnerability operates at the application layer and requires no authentication, making it particularly dangerous for publicly accessible VNC servers.
From an operational perspective, this vulnerability poses substantial risk to organizations relying on TigerVNC for remote desktop access, particularly in environments where VNC servers are exposed to untrusted networks. The remote exploit capability means that attackers can leverage this vulnerability from outside the network perimeter without requiring prior access credentials, potentially leading to complete system compromise. Attackers could execute malicious code with the privileges of the VNC server process, which typically runs with elevated permissions on the target system, potentially enabling lateral movement and persistent access within the network.
The impact of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and can be mapped to ATT&CK technique T1203, representing legitimate user access for remote code execution. Organizations should prioritize immediate patching of affected TigerVNC installations to version 1.10.1 or later, which includes proper bounds checking and memory validation in the TightDecoder::FilterGradient function. Additional mitigations should include network segmentation, firewall rules restricting VNC server access, and implementing network monitoring to detect anomalous VNC protocol traffic patterns. Security teams should also consider implementing intrusion detection systems specifically configured to identify exploitation attempts targeting this vulnerability.
The vulnerability demonstrates the critical importance of proper memory management in network-facing applications, particularly those handling user-provided data streams. VNC implementations must ensure robust input validation and bounds checking to prevent similar buffer overflow conditions in compression and decompression routines. Organizations should conduct comprehensive vulnerability assessments of their remote access infrastructure and implement regular security updates to address similar issues in other remote desktop protocols and VNC implementations that may share similar architectural patterns and code structures.