CVE-2026-107613 in TightVNC
Summary
by MITRE • 10/08/2026
A NULL pointer dereference vulnerability in the Win8ScreenDriver component of GlavSoft TightVNC Server for Windows before 2.8.88 allows an attacker to crash the server, causing a denial of service. When re-initialization of the DXGI Desktop Duplication driver fails in applyNewScreenProperties() (for example after a GPU reset, display hot-plug or session change), m_drvImpl is left NULL and is subsequently dereferenced without a check by executeDetection(), getScreenBuffer(), grabFb(), getScreenPropertiesChanged() and getCursorPosition().
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Analysis
by VulDB Data Team • 10/08/2026
The vulnerability identified in GlavSoft TightVNC Server for Windows prior to version 2.8.88 represents a critical stability issue rooted in improper input validation and null pointer handling within the Win8ScreenDriver component. This specific flaw allows an attacker who can trigger certain system-level events, such as GPU resets, display hot-plugs, or session changes, to cause a denial of service against the VNC server application. The core technical failure occurs during the re-initialization process of the DXGI Desktop Duplication driver when invoked by the applyNewScreenProperties function. Under normal operational conditions, this component manages screen capture and transmission for remote desktop sessions. However, if the initialization sequence fails due to external hardware or session state changes, the internal implementation pointer, designated as m_drvImpl, is left in a null state rather than being reset to a valid object or handled gracefully through error recovery mechanisms.
The severity of this vulnerability stems from multiple subsequent function calls that assume the presence of a valid driver instance without performing necessary safety checks. Specifically, functions such as executeDetection, getScreenBuffer, grabFb, getScreenPropertiesChanged, and getCursorPosition all attempt to dereference m_drvImpl directly. Because these methods are part of the active screen capture loop or event handling routine, they may be invoked immediately following a failed re-initialization sequence. When any of these functions access members or call virtual methods on the null pointer, it results in an immediate exception that crashes the TightVNC server process. This behavior effectively terminates all remote desktop sessions hosted by the application, leading to a complete loss of availability for users relying on the service.
From a classification perspective, this vulnerability aligns with CWE-476, which denotes NULL Pointer Dereference. The root cause is categorized under CWE-252, Unchecked Return Value, as the system fails to verify the success or failure status of the driver re-initialization before proceeding with operations that depend on its integrity. In terms of adversarial tactics, this flaw can be exploited via ATT&CK technique T1499, Endpoint Denial of Service, where an attacker leverages local access or specific trigger conditions to disrupt service availability rather than gaining unauthorized control over the system. The attack vector typically requires physical proximity or existing user-level privileges on the target machine to induce the triggering events like display hot-plugging or session switching that lead to the driver failure state.
Mitigation strategies for this vulnerability primarily involve upgrading to GlavSoft TightVNC Server version 2.8.88 or later, where these null pointer checks have been implemented within the affected functions. Until an upgrade is feasible, administrators should consider restricting physical access to systems running vulnerable versions of the software and disabling unnecessary display hot-plug detection if possible through group policy settings. Additionally, implementing monitoring solutions that detect unexpected process terminations in real-time can help identify exploitation attempts quickly. It is also advisable to ensure that GPU drivers are up-to-date, as certain driver bugs may exacerbate the frequency of initialization failures that trigger this code path. Regular patch management and adherence to vendor security advisories remain the most effective defense against such implementation flaws in remote access tools.