CVE-2024-9114: FastStone Image Viewer RCE Vulnerability

CVE-2024-9114 Overview

CVE-2024-9114 is an out-of-bounds write vulnerability [CWE-787] in FastStone Image Viewer. The flaw resides in the application's GIF file parsing routines. Attackers can trigger the issue by convincing a user to open a crafted GIF file or visit a malicious page hosting one. Successful exploitation allows arbitrary code execution in the context of the current user process. The vulnerability was reported through the Zero Day Initiative as ZDI-CAN-25145 and published as ZDI-24-1275.

Critical Impact
Remote attackers can execute arbitrary code on affected FastStone Image Viewer installations when a user opens a malicious GIF file.

Affected Products

FastStone Image Viewer 7.8
Earlier FastStone Image Viewer versions processing GIF files with the same parser
Windows systems where the vulnerable viewer is installed

Discovery Timeline

2024-11-22 - CVE-2024-9114 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-9114

Vulnerability Analysis

The vulnerability exists in FastStone Image Viewer's GIF file parser. The parser fails to validate user-supplied data from crafted GIF structures before writing to an allocated buffer. This missing bounds check results in a write past the end of the buffer. Attackers who control the overflowed memory can steer execution flow and run arbitrary code inside the viewer process.

The issue maps to Common Weakness Enumeration [CWE-787] Out-of-Bounds Write. The EPSS probability is 0.362% as of 2026-08-17, reflecting limited public exploitation activity to date.

Root Cause

The parser trusts length or offset values embedded in the GIF file without verifying them against the size of the destination buffer. When the crafted values exceed buffer boundaries, subsequent write operations corrupt adjacent memory. Corrupted heap or stack structures allow the attacker to influence control-flow data such as function pointers or return addresses.

Attack Vector

Exploitation requires user interaction. The target must open a malicious GIF file directly in FastStone Image Viewer or visit a page that delivers such a file to the viewer. No network privileges or authentication are required on the target system. The attack is local in scope, with the payload executing under the privileges of the user running the viewer. Full technical write-up is available in the Zero Day Initiative advisory ZDI-24-1275.

// No verified public proof-of-concept code is available.
// See ZDI-24-1275 for the vendor-coordinated technical description.

Detection Methods for CVE-2024-9114

Indicators of Compromise

GIF files opened by FSViewer.exe immediately preceding process crashes, unexpected child processes, or shellcode-like memory regions
New or unusual child processes spawned by FSViewer.exe, such as cmd.exe, powershell.exe, or scripting hosts
Outbound network connections from FSViewer.exe to untrusted hosts following image file access
Windows Error Reporting entries showing access violations in FastStone Image Viewer during GIF parsing

Detection Strategies

Alert on abnormal process lineage where FSViewer.exe becomes the parent of interactive shells or living-off-the-land binaries
Hunt for GIF files delivered via email, chat, or web download that are subsequently opened by FastStone Image Viewer
Correlate image file open events with in-memory execution indicators such as VirtualAlloc with PAGE_EXECUTE_READWRITE in FSViewer.exe

Monitoring Recommendations

Enable process creation, image load, and file open telemetry from endpoints running FastStone Image Viewer
Track version inventory of FSViewer.exe across managed endpoints to identify vulnerable hosts
Monitor endpoint crash telemetry for repeated faults in the GIF parsing code paths

How to Mitigate CVE-2024-9114

Immediate Actions Required

Update FastStone Image Viewer to the latest version released by the vendor once available
Restrict opening of GIF files from untrusted sources such as email attachments and unknown websites
Remove FastStone Image Viewer from systems where it is not required for business use
Apply application allowlisting to control which image viewers can execute on managed endpoints

Patch Information

At the time of publication, no vendor advisory URL is listed in the NVD entry. Administrators should consult the FastStone Soft website for the newest release and apply it as soon as it addresses the GIF parsing flaw. Refer to the Zero Day Initiative advisory ZDI-24-1275 for coordinated disclosure status.

Workarounds

Set a different default application for GIF files until a fixed version is confirmed
Block delivery of GIF attachments from external senders at the mail gateway where feasible
Run FastStone Image Viewer under a low-privileged user account to limit the impact of successful exploitation
Enable Data Execution Prevention and Address Space Layout Randomization system-wide to raise the cost of exploitation

bash

# Windows: change the default application association for .gif files
# Run in an elevated PowerShell session to inspect the current handler
Get-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.gif\UserChoice' -ErrorAction SilentlyContinue

# Then reassign .gif via Settings > Apps > Default apps, or use a Group Policy
# preference to enforce a non-vulnerable default viewer across the fleet.