CVE-2018-20024 in LibVNC
Summary
by MITRE
LibVNC before commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7 contains null pointer dereference in VNC client code that can result DoS.
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Analysis
by VulDB Data Team • 06/20/2023
The vulnerability identified as CVE-2018-20024 affects LibVNC versions prior to commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7 and represents a critical null pointer dereference flaw within the VNC client implementation. This issue resides in the client-side codebase of the LibVNC library, which is widely used for remote desktop access and virtual network computing operations. The vulnerability manifests when the client processes certain malformed or unexpected network packets, leading to a scenario where a null pointer is dereferenced during the processing of VNC protocol messages. Such a condition typically occurs when the application attempts to access memory through a pointer that has not been properly initialized or has been set to null, resulting in an immediate application crash or termination.
The technical exploitation of this vulnerability requires an attacker to establish a connection to a vulnerable VNC client and send specifically crafted packets that trigger the null pointer dereference condition. This type of flaw falls under CWE-476, which specifically addresses NULL Pointer Dereference, and represents a classic example of improper input validation in network protocol implementations. The vulnerability is particularly concerning because it can be triggered remotely without requiring authentication, making it a prime candidate for denial-of-service attacks against VNC client applications. When exploited successfully, the vulnerability results in a complete denial-of-service condition where the targeted VNC client application terminates unexpectedly, rendering the remote desktop session unavailable to legitimate users.
The operational impact of CVE-2018-20024 extends beyond simple service disruption, as it can be leveraged in broader attack scenarios within the context of the MITRE ATT&CK framework under the T1499 category for Network Denial of Service. Organizations relying on LibVNC for remote access and system administration are particularly vulnerable, as attackers could use this flaw to disrupt critical remote access capabilities. The vulnerability affects various implementations of LibVNC across different operating systems and platforms, including but not limited to Linux, Windows, and macOS environments where VNC clients are deployed. This widespread impact makes the vulnerability particularly dangerous in enterprise environments where multiple systems may be running vulnerable versions of the library, potentially allowing attackers to target multiple endpoints simultaneously.
Mitigation strategies for this vulnerability primarily involve updating to a patched version of LibVNC that includes the fix committed as 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7. System administrators should prioritize patching affected installations, particularly those running VNC client software in production environments. Additional defensive measures include network segmentation to limit exposure, implementing intrusion detection systems to monitor for suspicious VNC traffic patterns, and deploying network access controls that restrict VNC client connections to trusted networks only. The vulnerability also highlights the importance of proper input validation and error handling in network protocol implementations, aligning with security best practices outlined in various cybersecurity frameworks including NIST SP 800-53 and ISO 27001 standards. Organizations should conduct vulnerability assessments to identify all systems running vulnerable versions of LibVNC and implement comprehensive monitoring to detect potential exploitation attempts.