CVE-2026-101205 in Image Viewer
Summary
by MITRE • 09/29/2026
A vulnerability was determined in FastStone Image Viewer up to 8.3. This impacts an unknown function of the component PCX Decoder. This manipulation causes out-of-bounds read. The attack may be initiated 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 within FastStone Image Viewer, specifically affecting versions up to 8.3, resides in the PCX image decoder component. This software is widely used for viewing and editing images, and its ability to parse various file formats is critical to its functionality. The specific flaw lies in an unknown function responsible for handling PCX files, which are a raster graphics format originally developed by ZSoft Corporation. When processing maliciously crafted or corrupted PCX files, the decoder fails to properly validate input data boundaries before reading from memory. This lack of rigorous bounds checking leads directly to an out-of-bounds read condition. In cybersecurity terms, this is classified under CWE-125, which describes Out-of-Bounds Read vulnerabilities where a program reads data past the end or before the beginning of the intended buffer. Such flaws are particularly dangerous because they can lead to information disclosure, allowing attackers to leak sensitive memory contents that may include passwords, encryption keys, or other proprietary data stored in adjacent memory locations.
The operational impact of this vulnerability is significant due to its potential for remote initiation. Although FastStone Image Viewer is primarily a desktop application, the attack vector being described as remote suggests that an attacker could potentially trigger the exploit through mechanisms such as embedding malicious PCX files in emails, hosting them on compromised websites accessed via browser plugins or integrated viewers, or distributing them through file-sharing platforms. If successful, this out-of-bounds read does not necessarily lead to arbitrary code execution immediately, but it serves as a powerful tool for reconnaissance and information gathering. An attacker could use the leaked memory data to map the victim's system environment, identify installed software versions, or extract credentials that might be cached in memory by other applications running on the same machine. This aligns with ATT&CK technique T1005, which covers Data from Local System, indicating that the vulnerability facilitates unauthorized access to local information without requiring direct user interaction beyond opening a file.
The response from the vendor regarding this disclosure has been notably absent. Despite being contacted early about the security flaw, there has been no acknowledgment or patch released by the developers of FastStone Image Viewer. This lack of remediation places the burden of mitigation squarely on the end-users and system administrators who rely on this software. In such scenarios where a vendor is unresponsive to responsible disclosure efforts, organizations must adopt alternative defensive strategies to protect their assets. One primary approach involves implementing strict file type filtering at network boundaries using firewalls or intrusion prevention systems that block PCX files from entering internal networks unless absolutely necessary for business operations. Additionally, application whitelisting can be employed to prevent the execution of unauthorized versions of image viewers if they are not part of a sanctioned software list.
For individual users and IT departments continuing to use FastStone Image Viewer despite the known vulnerability, several mitigations should be considered to reduce risk exposure. Users should exercise extreme caution when opening PCX files obtained from untrusted sources or received via email attachments. Enabling macro security settings in associated office applications that might embed images can also help prevent accidental execution of malicious payloads if they are disguised as image files. Furthermore, keeping antivirus and endpoint detection and response solutions updated is crucial, as these tools may have signatures capable of detecting the exploitation patterns associated with out-of-bounds reads in common libraries used by such viewers. Since no patch exists, users should evaluate whether alternative image viewing software that has a more active security maintenance schedule can serve as a viable replacement for their workflow needs. Until the vendor addresses this issue or provides an update, treating all PCX files as potentially hostile remains the most prudent course of action to maintain system integrity and confidentiality.