CVE-2020-29260 in libvncclient
Summary
by MITRE • 09/03/2022
libvncclient v0.9.13 was discovered to contain a memory leak via the function rfbClientCleanup().
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Analysis
by VulDB Data Team • 07/26/2025
The vulnerability identified as CVE-2020-29260 affects libvncclient version 0.9.13 and represents a memory leak condition within the rfbClientCleanup() function. This memory leak occurs during the cleanup process of VNC client connections, which can lead to progressive memory consumption over time. The issue is particularly concerning in environments where VNC client applications are frequently established and terminated, as the leaked memory is not properly released back to the operating system. The vulnerability stems from improper memory management within the cleanup routine, where allocated memory blocks are not correctly deallocated when the client connection is terminated.
The technical flaw manifests when the rfbClientCleanup() function fails to release all memory resources that were allocated during the VNC client initialization and connection establishment phases. This memory leak can be triggered whenever a VNC client application terminates its connection to a remote desktop server, particularly in scenarios involving multiple rapid connection attempts or long-running client processes. The vulnerability is classified as a memory leak under CWE-401, which specifically addresses improper deallocation of memory resources. This weakness directly impacts the memory management practices within the VNC client implementation and can result in gradual system resource exhaustion over time.
The operational impact of this vulnerability extends beyond simple resource consumption issues and can significantly affect system stability and performance in production environments. When multiple VNC client connections are established and terminated frequently, the cumulative effect of memory leaks can lead to system slowdowns, application crashes, or even complete system memory exhaustion. This is particularly problematic in server environments where VNC clients are used for remote administration, as the vulnerability can be exploited to cause denial of service conditions. The memory leak can also be amplified in automated systems where VNC client connections are programmatically managed and frequently cycled, leading to progressive degradation of system performance.
Mitigation strategies for CVE-2020-29260 should focus on immediate patching of the affected libvncclient library to version 0.9.14 or later, which contains the corrected memory management implementation. Organizations should implement monitoring systems to track memory usage patterns of VNC client processes and establish alerting mechanisms for unusual memory consumption trends. Network administrators should consider implementing connection limiting measures to prevent excessive concurrent VNC client connections that could exacerbate the memory leak conditions. The vulnerability can be mapped to ATT&CK technique T1499.004, which covers resource exhaustion attacks through memory leaks, and represents a classic example of how improper memory management can create persistent security weaknesses in network client applications. System administrators should also consider implementing automated restart procedures for VNC client services to mitigate the impact of memory leaks, while ensuring that proper application logging is maintained to track connection patterns and memory usage metrics.