CVE-2018-20022 in LibVNC
Summary
by MITRE
LibVNC before 2f5b2ad1c6c99b1ac6482c95844a84d66bb52838 contains multiple weaknesses CWE-665: Improper Initialization vulnerability in VNC client code that allows attacker to read stack memory and can be abuse for information disclosure. Combined with another vulnerability, it can be used to leak stack memory layout and in bypassing ASLR
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Analysis
by VulDB Data Team • 06/20/2023
The vulnerability identified as CVE-2018-20022 affects LibVNC versions prior to commit 2f5b2ad1c6c99b1ac6482c95844a84d66bb52838 and represents a critical improper initialization flaw within the VNC client codebase. This vulnerability is categorized under CWE-665, which specifically addresses improper initialization conditions that can lead to security weaknesses. The flaw manifests in how the VNC client handles memory allocation and initialization during the connection process, creating opportunities for malicious actors to exploit the system's memory management mechanisms.
The technical exploitation of this vulnerability enables attackers to read stack memory contents through the improperly initialized client components. When the VNC client establishes connections or processes certain network responses, it fails to properly initialize memory regions that should contain sensitive data or control information. This improper initialization creates memory access patterns that can be manipulated by remote attackers to extract information from the stack memory. The vulnerability specifically impacts the VNC client implementation where memory buffers are not adequately cleared or initialized before use, allowing for information disclosure through memory reads.
The operational impact of this vulnerability extends beyond simple information disclosure to include more sophisticated attack vectors. Attackers can leverage this weakness to leak stack memory layout information, which provides crucial details about the memory organization and can be used to bypass important security mechanisms such as Address Space Layout Randomization. The ability to extract stack memory contents means that attackers can potentially discover memory addresses, function pointers, and other sensitive information that would normally be protected by proper memory initialization. This information leakage creates a foundation for more advanced exploitation techniques and significantly reduces the security posture of systems using vulnerable LibVNC implementations.
The combination of this vulnerability with other existing weaknesses in the VNC client creates a particularly dangerous attack scenario that can be used to circumvent modern security protections. When paired with other memory-related vulnerabilities, the improper initialization flaw becomes a critical component in bypassing ASLR, which is a fundamental defense mechanism designed to randomize memory layout addresses to prevent exploitation. The stack memory leakage allows attackers to determine the base addresses of various memory regions, effectively neutralizing ASLR protections and making subsequent exploitation attempts much more successful. This vulnerability demonstrates how seemingly minor initialization flaws can have cascading effects on overall system security.
Mitigation strategies for this vulnerability require immediate patching of LibVNC implementations to the fixed version containing commit 2f5b2ad1c6c99b1ac6482c95844a84d66bb52838 or equivalent fixes. Organizations should conduct thorough inventory checks to identify all systems utilizing vulnerable LibVNC versions and implement the necessary updates as quickly as possible. Additionally, network segmentation and access controls should be strengthened to limit exposure to potential attackers, particularly in environments where VNC services are exposed to untrusted networks. Security monitoring should be enhanced to detect unusual memory access patterns or network traffic that might indicate exploitation attempts. The vulnerability highlights the importance of proper memory initialization practices in security-critical code and underscores the need for comprehensive code reviews focusing on initialization sequences and memory management practices. Organizations should also consider implementing additional security controls such as stack canaries and other memory protection mechanisms to provide defense-in-depth against similar vulnerabilities.