CVE-2026-101204 in Image Viewer
Summary
by MITRE • 09/29/2026
A vulnerability was found in FastStone Image Viewer up to 8.3. This affects an unknown function of the file FSViewer.exe of the component TGA Image Handler. The manipulation results in out-of-bounds read. The attack can be launched 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 • 09/29/2026
The vulnerability identified in FastStone Image Viewer versions up to 8.3 represents a significant security risk within the application's image processing subsystem, specifically targeting the TGA (Truevision TARGA) image handler component embedded within the FSViewer.exe executable. This flaw is classified as an out-of-bounds read, which falls under the Common Weakness Enumeration category CWE-125. An out-of-bounds read occurs when a program attempts to access memory locations that are outside the boundaries of allocated buffers or arrays. In the context of image viewers, this typically happens during the parsing and decoding of image file headers or pixel data structures. When FastStone Image Viewer processes a maliciously crafted TGA file, it fails to adequately validate the dimensions, color depth, or other metadata fields contained within the file header before attempting to read corresponding data from memory. This lack of rigorous boundary checking allows an attacker to trigger access to sensitive areas of the application's virtual address space that were not intended for reading by this specific function.
The operational impact of this vulnerability is primarily centered on information disclosure and potential system instability, although it can also serve as a precursor to more severe exploits such as remote code execution depending on how the leaked memory contents are utilized in subsequent operations. Because the flaw results in an out-of-bounds read rather than a write operation, direct arbitrary code execution via buffer overflow is less likely, but the leakage of heap or stack data poses serious privacy and security concerns. An attacker can potentially extract sensitive information stored in adjacent memory regions, such as cryptographic keys, authentication tokens, or other user-specific data that resides near the image processing buffers. Furthermore, reading invalid memory addresses often leads to application crashes, resulting in a denial-of-service condition for legitimate users who attempt to open compromised files. The ability to launch this attack remotely means that an adversary does not need physical access to the target system; instead, they can distribute malicious TGA images through email attachments, web pages, or file-sharing platforms, relying on social engineering or drive-by download techniques to trick a user into opening the file with FastStone Image Viewer.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1203, which covers Exploitation for Client Execution, as well as aspects of data exfiltration if sensitive memory contents are successfully retrieved and transmitted back to an attacker-controlled server. The fact that the vendor was contacted early regarding this disclosure but failed to respond highlights a critical gap in the security lifecycle management of the software. Without official patches or updates from FastStone, users remain exposed indefinitely. This lack of remediation support forces organizations relying on this tool for image viewing and basic editing tasks to seek alternative solutions or implement strict network-level controls to mitigate risk.
To mitigate the risks associated with this vulnerability in the absence of a vendor patch, several defensive measures should be implemented immediately. The most effective strategy is to replace FastStone Image Viewer with a modern, actively maintained alternative that adheres to secure coding practices and receives regular security updates. If migration is not immediately feasible, users should exercise extreme caution when opening image files from untrusted sources, avoiding the use of FastStone for viewing images downloaded from the internet or received via email. Additionally, deploying application whitelisting solutions can prevent unauthorized execution of FSViewer.exe if it is not a critical business requirement. Network segmentation and strict egress filtering can also help limit the impact by preventing any potential data exfiltration should an attacker manage to exploit the memory leak for information gathering purposes. Ultimately, given the vendor's non-responsiveness, treating this software as compromised in untrusted environments is the most prudent course of action until a verified patch becomes available or the application is deprecated entirely.