CVE-2018-21247 in LibVNCServer
Summary
by MITRE
An issue was discovered in LibVNCServer before 0.9.13. There is a memory leak in the libvncclient/rfbproto.c ConnectToRFBRepeater function.
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Analysis
by VulDB Data Team • 06/18/2020
The vulnerability identified as CVE-2018-21247 represents a critical memory management flaw within LibVNCServer versions prior to 0.9.13. This issue specifically affects the libvncclient/rfbproto.c component where the ConnectToRFBRepeater function fails to properly release allocated memory resources. The memory leak occurs during the process of establishing connections to RFB repeaters, which are essential components in virtual network computing environments that facilitate connections through intermediate servers. This flaw impacts the overall stability and performance of systems utilizing LibVNCServer for remote desktop access and virtualization services.
The technical implementation of this vulnerability stems from improper memory deallocation within the connection establishment sequence. When the ConnectToRFBRepeater function processes connection requests to RFB repeaters, it allocates memory for various data structures including connection handles, buffer allocations, and protocol state information. However, the function does not consistently free these allocated memory blocks when connection attempts fail or when the connection process completes, leading to gradual memory consumption over time. This memory leak pattern is particularly concerning in long-running applications or services where repeated connection attempts occur, as it can eventually lead to system resource exhaustion and service degradation.
The operational impact of this vulnerability extends across multiple security domains and system environments where LibVNCServer is deployed. Organizations utilizing virtual desktop infrastructure, remote access solutions, and network computing services may experience gradual performance degradation, system instability, and potential service interruptions due to the accumulating memory consumption. The vulnerability can be exploited by malicious actors who repeatedly attempt connections to trigger the memory leak, potentially leading to denial of service conditions that affect legitimate users. Additionally, this flaw may compound other security issues within the system as resource exhaustion can mask or amplify existing vulnerabilities. The memory leak affects both client and server components of the VNC protocol implementation, making it a systemic concern for all systems relying on LibVNCServer for remote access capabilities.
Mitigation strategies for CVE-2018-21247 focus primarily on immediate software updates and system hardening measures. Organizations should prioritize upgrading to LibVNCServer version 0.9.13 or later, which contains the patched implementation of the ConnectToRFBRepeater function with proper memory deallocation routines. System administrators should implement monitoring solutions to track memory usage patterns and detect anomalous consumption that may indicate exploitation attempts. Network segmentation and access controls should be strengthened to limit exposure of vulnerable systems to potential attackers. The vulnerability aligns with CWE-401, which specifically addresses improper resource management and memory leaks in software implementations. From an attack framework perspective, this issue can be categorized under the denial of service category within the MITRE ATT&CK framework, potentially enabling broader exploitation tactics when combined with other vulnerabilities in the system architecture. Regular security assessments and vulnerability scanning should be conducted to identify systems running vulnerable versions of LibVNCServer and ensure comprehensive remediation across all networked environments.