CVE-2018-15127 in LibVNC
Summary
by MITRE
LibVNC before commit 502821828ed00b4a2c4bef90683d0fd88ce495de contains heap out-of-bound write vulnerability in server code of file transfer extension that can result remote code execution
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 06/19/2023
The vulnerability identified as CVE-2018-15127 represents a critical heap out-of-bounds write flaw within the LibVNC library's server implementation, specifically affecting the file transfer extension functionality. This vulnerability exists in LibVNC versions prior to commit 502821828ed00b4a2c4bef90683d0fd88ce495de, making it a software flaw that has persisted across multiple releases and potentially affected numerous systems relying on this popular open-source VNC implementation. The vulnerability is particularly concerning as it resides within the server code of the file transfer extension, which is a core functionality that enables file operations between VNC clients and servers.
The technical nature of this vulnerability stems from improper bounds checking within the memory allocation and handling mechanisms of the file transfer extension. When processing file transfer requests, the server code fails to validate the size or boundaries of data structures before writing to heap memory locations, creating an opportunity for attackers to manipulate memory layout and potentially execute arbitrary code. This heap out-of-bounds write condition typically occurs when the application writes data beyond the allocated memory boundaries, which can overwrite adjacent memory locations and corrupt program execution flow. The flaw aligns with CWE-787, which specifically addresses out-of-bounds write vulnerabilities that can lead to memory corruption and arbitrary code execution.
The operational impact of this vulnerability extends beyond simple remote code execution, as it provides attackers with a potential pathway for complete system compromise. An attacker who can establish a connection to a vulnerable LibVNC server and initiate file transfer operations could potentially exploit this vulnerability to execute malicious code with the privileges of the VNC server process. This could result in unauthorized access to systems, data exfiltration, privilege escalation, or even persistent backdoor installation. The vulnerability affects any system running vulnerable versions of LibVNC that have file transfer extensions enabled, which includes numerous enterprise VNC implementations and remote desktop solutions.
Mitigation strategies for CVE-2018-15127 should prioritize immediate patching of affected LibVNC installations to the version containing the fix from commit 502821828ed00b4a2c4bef90683d0fd88ce495de. Organizations should also implement network segmentation and access controls to limit exposure of VNC services to untrusted networks, as recommended by ATT&CK technique T1021.001 for remote services. Additional defensive measures include disabling file transfer extensions when not required, implementing network monitoring to detect anomalous file transfer activities, and conducting regular vulnerability assessments of VNC implementations. The vulnerability demonstrates the critical importance of proper input validation and memory safety practices in server-side applications, particularly those handling network communications and file operations that are frequently targeted by attackers seeking remote code execution capabilities.