CVE-2026-116463 in Image Viewer
Summary
by MITRE • 10/26/2026
A vulnerability was identified in FastStone Image Viewer up to 8.5. Affected is the function FUN_0062d96c of the component Box-Average Downsampler Engine. The manipulation leads to out-of-bounds read. It is possible to initiate the attack remotely. The vendor was contacted early about this disclosure but did not respond in any way.
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Analysis
by VulDB Data Team • 10/26/2026
The vulnerability identified within FastStone Image Viewer, specifically affecting versions up through 8.5, represents a critical security flaw located in the Box-Average Downsampler Engine component. This engine is responsible for processing image data to reduce resolution or dimensions during viewing and editing operations. The specific point of failure resides in function FUN_0062d96c, which handles memory access patterns when calculating average pixel values across defined regions. When an attacker provides a specially crafted input file containing malformed metadata or corrupted dimension parameters, the application fails to properly validate boundary conditions before accessing memory buffers. This lack of rigorous bounds checking results in an out-of-bounds read operation, where the software attempts to retrieve data from memory locations that lie outside the allocated buffer space designated for image processing tasks.
From a technical perspective, this flaw is classified under CWE-125, which denotes Out-of-Bounds Read vulnerabilities. The core issue stems from insufficient validation of array indices or pointer arithmetic during the downsampling calculation process. In typical execution flows, when an image with specific width and height attributes triggers the average box algorithm, the internal logic calculates memory offsets based on these dimensions. If the input data contains values that exceed expected limits due to truncation errors, integer overflows, or deliberate manipulation by a malicious actor, the resulting pointer arithmetic will reference invalid memory addresses. While out-of-bounds reads are often considered less severe than writes because they do not directly allow for arbitrary code execution via stack corruption, they remain highly dangerous in modern software environments. The primary risk associated with this type of vulnerability is information disclosure, where sensitive data residing adjacent to the target buffer can be leaked into the application's memory space and potentially exfiltrated by an attacker controlling the process context.
The operational impact of this vulnerability is significantly amplified by its remote exploitability vector. Although FastStone Image Viewer is primarily a desktop-based image management tool, users frequently encounter such files through email attachments, downloaded archives from untrusted sources, or even embedded within web pages if browser plugins are involved. An attacker can distribute a maliciously crafted image file that triggers the flaw upon opening in the affected version of the software. Upon execution, the out-of-bounds read may cause the application to crash due to access violations, leading to denial of service conditions for legitimate users. More critically, depending on the compiler optimizations and memory layout of the specific system architecture, this vulnerability could potentially be leveraged as part of a larger attack chain. For instance, it might facilitate information leakage that aids in bypassing security mitigations such as Address Space Layout Randomization (ASLR) or Data Execution Prevention (DEP), thereby setting the stage for more severe exploits like remote code execution if combined with other memory corruption techniques.
In terms of threat modeling and industry standards, this vulnerability aligns with ATT&CK technique T1059, specifically sub-techniques related to command and script interpreters or operating system APIs that could be abused during exploitation phases following initial access via the malicious file. The fact that the vendor was contacted early regarding this disclosure but failed to respond indicates a lack of active security maintenance for older versions of the software. This absence of patching support leaves users exposed indefinitely, as there is no official fix available from the developer. Consequently, organizations and individual users relying on FastStone Image Viewer must treat any incoming image files with extreme caution, particularly those originating from untrusted networks or unknown senders.
Mitigation strategies for this vulnerability are primarily defensive in nature due to the lack of vendor patches. Users should immediately consider migrating to alternative image viewers that have active security support and regular update cycles. If migration is not feasible, strict file filtering policies should be implemented at the network perimeter using email gateways or web proxies to inspect incoming images for anomalies in header structures and dimension values before they reach end-user systems. Additionally, enabling application whitelisting can prevent unauthorized execution of modified binaries if attackers attempt to replace legitimate executables alongside malicious payloads. For advanced protection, deploying endpoint detection and response solutions that monitor for unusual memory access patterns or process behavior associated with image processing libraries can help detect exploitation attempts in real-time. Ultimately, the responsibility falls on users to maintain awareness of software lifecycle status and avoid using discontinued applications for handling untrusted digital content.