CVE-2017-5885 in gtk-vnc
Summary
by MITRE
Multiple integer overflows in the (1) vnc_connection_server_message and (2) vnc_color_map_set functions in gtk-vnc before 0.7.0 allow remote servers to cause a denial of service (crash) or possibly execute arbitrary code via vectors involving SetColorMapEntries, which triggers a buffer overflow.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability identified as CVE-2017-5885 represents a critical security flaw in the gtk-vnc library version 0.7.0 and earlier, affecting virtual network computing implementations that rely on this graphical toolkit component. This issue manifests through two distinct integer overflow conditions within the library's server message handling mechanisms, specifically impacting the vnc_connection_server_message and vnc_color_map_set functions. The vulnerability stems from inadequate input validation when processing color map entries during VNC server communications, creating a pathway for remote attackers to manipulate memory structures through crafted SetColorMapEntries protocol messages.
The technical exploitation of this vulnerability occurs when a remote VNC server sends maliciously formatted color map entries that trigger integer overflows in the affected functions. These integer overflows result in buffer overflow conditions that can corrupt memory layout and potentially allow arbitrary code execution. The flaw specifically affects the gtk-vnc library's handling of color map entries, where the library fails to properly validate the size parameters of incoming color map data before attempting to allocate memory buffers. This lack of proper bounds checking creates a scenario where an attacker can manipulate the integer values to cause memory corruption that leads to program termination or code execution.
From an operational perspective, this vulnerability poses significant risks to systems utilizing gtk-vnc for VNC client implementations, particularly in enterprise environments where remote desktop access is prevalent. The denial of service aspect can disrupt legitimate remote access sessions, while the potential for arbitrary code execution opens pathways for attackers to gain unauthorized access to systems. The vulnerability affects both the stability and security posture of VNC implementations, as it can be exploited remotely without requiring authentication. Organizations using VNC-based remote access solutions are particularly vulnerable since the attack can be executed through the VNC protocol itself, making it difficult to distinguish between legitimate and malicious traffic.
The impact of this vulnerability aligns with CWE-190, which describes integer overflow conditions that can lead to buffer overflows and memory corruption. The flaw demonstrates characteristics consistent with the ATT&CK framework's privilege escalation and denial of service techniques, as attackers can leverage the vulnerability to either crash services or execute malicious code on target systems. The vulnerability affects the integrity and availability of VNC implementations, making it a critical concern for security operations teams managing remote access infrastructure. Organizations should prioritize patching this vulnerability through updates to the gtk-vnc library to version 0.7.0 or later, which contains the necessary fixes for integer overflow protections. Additionally, network segmentation and monitoring of VNC traffic can help detect and prevent exploitation attempts, while implementing proper access controls and authentication mechanisms provides additional defense layers against potential attackers targeting this specific vulnerability.