CVE-2026-107614
Received Received - Intake

Integer Underflow in TightVNC Server for Windows

Publication date: 2026-10-08

Last updated on: 2026-10-08

Assigner: securin

Description
An integer underflow in WinCursorShapeUtils::trimTransparent() in GlavSoft TightVNC Server for Windows before 2.8.88 allows a local authenticated user to crash the server, and potentially read out-of-bounds memory, by causing a cursor shape with a width or height of zero to be processed on the DXGI capture path. The loop bound width - 1 wraps to 0xFFFFFFFF, producing an access roughly 4 GB beyond the 64 KB cursor buffer; a monochrome cursor of height 1 also becomes 0 because getCursorHeight() halves the height in place.

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Meta Information

Published
2026-10-08
Last Modified
2026-10-08
Generated
2026-10-08
AI Q&A
2026-10-08
EPSS Evaluated
N/A
NVD
CVE-2026-107614
EUVD
EUVD-2026-94978

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
GlavSoft TightVNC 0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-191 The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.
CWE-125 The product reads data past the end, or before the beginning, of the intended buffer.

Attack-Flow Graph

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Executive Summary

This vulnerability is an integer underflow in the WinCursorShapeUtils::trimTransparent() function of GlavSoft TightVNC Server for Windows versions before 2.8.88. It occurs when a local authenticated user causes a cursor shape with zero width or height to be processed on the DXGI capture path. This leads to a loop bound calculation wrapping to 0xFFFFFFFF, causing an out-of-bounds memory read approximately 4 GB beyond a 64 KB cursor buffer. Additionally, a monochrome cursor of height 1 becomes zero due to improper height calculation.

Detection Guidance

Detection requires checking if GlavSoft TightVNC Server for Windows versions before 2.8.88 are installed. Inspect installed software via system tools like 'wmic product get name' or 'Get-WmiObject -Class Win32_Product' on Windows. Verify running processes for 'tvnserver.exe' or similar.

Impact Analysis

This vulnerability can allow a local authenticated user to crash the TightVNC server and potentially read out-of-bounds memory. This could lead to unauthorized access to sensitive data, system instability, or further exploitation of the affected system.

Mitigation Strategies

Update GlavSoft TightVNC Server for Windows to version 2.8.88 or later immediately. If updating is not possible, disable the DXGI capture path or restrict local authenticated user access to the server. Monitor for crashes or unusual memory access patterns.

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