CVE-2017-7396 in TigerVNC
Summary
by MITRE
In TigerVNC 1.7.1 (CConnection.cxx CConnection::CConnection), an unauthenticated client can cause a small memory leak in the server.
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Analysis
by VulDB Data Team • 11/24/2022
The vulnerability identified as CVE-2017-7396 resides within TigerVNC version 1.7.1, specifically within the CConnection.cxx file in the CConnection::CConnection constructor. This memory leak occurs when an unauthenticated client establishes a connection to the VNC server, creating a subtle but persistent resource exhaustion issue that can degrade server performance over time. The flaw represents a classic case of insufficient resource management where the server fails to properly handle connection initialization from unauthorized clients.
The technical implementation of this vulnerability stems from the CConnection constructor's handling of client connection establishment without adequate validation of authentication status. When an unauthenticated client connects to the VNC server, the constructor allocates memory resources to process the connection attempt but fails to properly clean up or release these resources upon connection failure or authentication rejection. This memory allocation occurs in the server-side code that manages client connections, creating a small but persistent memory leak that accumulates with each failed connection attempt.
From an operational impact perspective, this vulnerability allows an attacker to perform a form of resource exhaustion attack against the VNC server by repeatedly connecting without authentication. While each individual memory leak is small, the cumulative effect of multiple connection attempts can gradually consume server memory resources, potentially leading to performance degradation, service disruption, or even complete server unresponsiveness. The vulnerability is particularly concerning in environments where VNC servers are exposed to the internet or where automated scanning tools might attempt to probe connections.
This vulnerability aligns with CWE-401, which describes improper management of dynamic resources, specifically focusing on memory leaks in software systems. The issue also relates to ATT&CK technique T1210, which involves exploitation of remote services through resource consumption attacks. The memory leak represents a denial of service vector that can be exploited without requiring sophisticated credentials or complex attack chains, making it particularly dangerous in environments where VNC servers are accessible to untrusted networks.
The recommended mitigation strategy involves upgrading to a patched version of TigerVNC that properly handles connection resource cleanup regardless of authentication status. Administrators should also implement network-level controls such as firewall rules to restrict VNC server access to trusted IP addresses only. Additionally, monitoring systems should be deployed to detect unusual connection patterns or memory usage spikes that might indicate exploitation attempts. The vulnerability highlights the importance of proper resource management in server-side applications and demonstrates how seemingly minor implementation flaws can create significant security concerns in remote access systems.