Critical Out-of-Bounds Write Vulnerability in FastStone Image Viewer

• •CVE-2026-101203 affects FastStone Image Viewer versions up to 8.3.
• •The vulnerability allows remote attackers to exploit an out-of-bounds write condition.
• •User interaction is required to trigger the vulnerability by opening crafted image files.

A vulnerability, CVE-2026-101203, has been identified in FastStone Image Viewer versions up to 8.3, specifically in the 1bpp RLE Decoder component. This out-of-bounds write vulnerability allows remote attackers to manipulate the application by sending specially crafted image files that require user interaction to open. The attack can lead to memory corruption, potentially compromising the application's integrity and availability. The vendor has been contacted but has not responded to the disclosure. The vulnerability was published on September 28, 2026, and is rated with a CVSS score of 6.3, indicating a high risk if left unpatched. Organizations are advised to avoid opening untrusted image files and to update the application once a patch is available. Currently, there is no evidence of public proof-of-concept exploitation. The attack complexity is low, and no privileges are required for exploitation.