CVE-2017-7395 in TigerVNC
Summary
by MITRE
In TigerVNC 1.7.1 (SMsgReader.cxx SMsgReader::readClientCutText), by causing an integer overflow, an authenticated client can crash the server.
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Analysis
by VulDB Data Team • 11/24/2022
The vulnerability identified as CVE-2017-7395 resides within TigerVNC version 1.7.1, specifically in the SMsgReader.cxx file within the SMsgReader::readClientCutText method. This issue represents a critical security flaw that demonstrates how improper input validation can lead to denial of service conditions in remote desktop software implementations. The vulnerability affects the VNC (Virtual Network Computing) protocol implementation that allows remote desktop access and control, making it particularly concerning for enterprise environments where remote access solutions are extensively deployed.
The technical flaw manifests as an integer overflow condition that occurs when processing client cut text data sent from an authenticated client to the VNC server. When a malicious client sends specially crafted data that triggers integer overflow during the processing of clipboard content, the server's memory management becomes compromised. This overflow condition causes the server application to crash and terminate unexpectedly, effectively rendering the remote desktop service unavailable to legitimate users. The vulnerability requires authentication to exploit, meaning that an attacker must first establish a valid session with the VNC server before being able to trigger the crash condition.
From an operational impact perspective, this vulnerability creates significant availability risks for systems relying on TigerVNC for remote access. The denial of service condition can be exploited by authenticated users who may have legitimate access to the system, making it particularly dangerous in environments where privilege escalation is possible. The crash typically results in complete service disruption requiring manual intervention to restart the VNC server process. This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which specifically addresses issues where integer arithmetic operations produce results that exceed the maximum value representable by the data type. The ATT&CK framework categorizes this as a Denial of Service technique under the T1499 sub-technique, where adversaries compromise system availability through resource exhaustion or application crashes.
The exploitation of this vulnerability demonstrates the importance of proper input validation in network protocols, particularly in applications handling user-supplied data. The integer overflow occurs during the processing of client cut text, which is a standard clipboard functionality in VNC implementations. This highlights how seemingly benign features can become attack vectors when proper boundary checks are not implemented. Organizations using TigerVNC should prioritize patching this vulnerability as it represents a straightforward path to service disruption that can be exploited by both malicious insiders and external attackers who have gained authentication credentials.
Mitigation strategies should include immediate deployment of the vendor-provided patch that addresses the integer overflow condition in the SMsgReader::readClientCutText method. Additionally, network segmentation and access controls should be implemented to limit exposure of VNC services to trusted networks only. Monitoring should be enhanced to detect unusual patterns in clipboard data processing that might indicate exploitation attempts. The vulnerability also underscores the need for comprehensive security testing of network protocols, particularly focusing on boundary conditions and input validation in all data processing paths. Organizations should consider implementing intrusion detection systems that can identify abnormal behavior patterns associated with VNC protocol exploitation attempts.