CVE-2026-40916: GIMP TIM Image Loader DoS Vulnerability

CVE-2026-40916 Overview

A stack buffer overflow vulnerability has been discovered in GIMP, the popular open-source image manipulation software. The flaw exists in the TIM image loader's 4BPP (4 bits per pixel) decoding path, where improper handling of image data can lead to an unconditional overflow when writing to a variable-length array. This vulnerability allows a local attacker to cause a Denial of Service (DoS) condition by tricking a user into opening a specially crafted TIM image file.

Critical Impact
Opening a maliciously crafted TIM image file causes GIMP to crash, resulting in loss of unsaved work and potential disruption to design workflows.

Affected Products

GIMP (GNU Image Manipulation Program)
Systems with GIMP installed that process TIM image files
Environments where users open untrusted image files

Discovery Timeline

April 15, 2026 - CVE-2026-40916 published to NVD
April 15, 2026 - Last updated in NVD database

Technical Details for CVE-2026-40916

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption flaw that occurs when the TIM image loader processes 4BPP encoded images. The TIM file format, originally developed for PlayStation graphics, contains indexed color data that GIMP must decode and convert for display.

The flaw manifests in the decoding routine responsible for unpacking 4-bit pixel data. When processing a malformed TIM file with manipulated header values or pixel data, the decoder writes beyond the boundaries of a stack-allocated buffer. Because the overflow is unconditional once triggered, any TIM file crafted to exploit this path will reliably crash the application.

The local attack vector requires user interaction—specifically, the victim must open the malicious file. This limits the attack surface to scenarios where an attacker can deliver a crafted TIM file to a target user through email attachments, file sharing, or other distribution methods.

Root Cause

The root cause stems from insufficient validation of image dimensions and pixel data in the TIM loader's 4BPP decoding function. The code allocates a variable-length array (VLA) on the stack based on image parameters but fails to properly validate these values against the actual buffer capacity. When the decoded pixel data exceeds the allocated array size, a stack buffer overflow occurs, corrupting adjacent stack memory and causing a crash.

Attack Vector

The attack requires local access and user interaction. An attacker must craft a malicious TIM image file with specific characteristics that trigger the vulnerable code path in the 4BPP decoder. The attack chain typically involves:

Creating a TIM file with manipulated header fields specifying large or malformed dimensions
Embedding pixel data designed to overflow the stack buffer during decoding
Delivering the malicious file to a victim through social engineering
Victim opens the file in GIMP, triggering the crash

The vulnerability results in application termination rather than code execution, as the overflow corrupts critical stack data leading to an immediate crash. For technical details on this vulnerability, refer to the Red Hat CVE-2026-40916 Advisory and Red Hat Bug Report #2458745.

Detection Methods for CVE-2026-40916

Indicators of Compromise

Unexpected GIMP crashes when opening TIM image files
Core dumps or crash reports referencing the TIM loader module
Presence of TIM files (.tim extension) from untrusted sources in user directories
Repeated application crashes from the same user processing image files

Detection Strategies

Monitor for GIMP process crashes with stack traces indicating memory corruption in image loading routines
Implement file type filtering to flag or quarantine TIM files from untrusted sources
Deploy endpoint detection rules for abnormal GIMP termination patterns
Use SentinelOne's behavioral AI to detect exploitation attempts targeting image processing applications

Monitoring Recommendations

Enable crash reporting and logging for GIMP installations in enterprise environments
Monitor file system activity for creation of .tim files in user download directories
Configure SIEM alerts for repeated GIMP crashes across multiple workstations
Track email attachments and file transfers containing TIM image formats

How to Mitigate CVE-2026-40916

Immediate Actions Required

Avoid opening TIM image files from untrusted or unknown sources until patches are applied
Configure email gateways to filter or warn on TIM file attachments
Educate users about the risks of opening unsolicited image files
Consider temporarily disabling TIM file support if not required for business operations

Patch Information

Security updates addressing this vulnerability should be obtained from your operating system's package repository or directly from the GIMP project. Check the Red Hat CVE-2026-40916 Advisory for Red Hat-specific patch information and availability. Monitor your distribution's security announcements for package updates containing the fix.

Workarounds

Use alternative image viewers that do not support TIM format for untrusted files
Implement file extension blocking for .tim files at the network perimeter
Run GIMP in a sandboxed environment when processing files from untrusted sources
Convert TIM files using command-line tools in isolated environments before opening in GIMP

bash

# Example: Block TIM files at download directory level (Linux)
# Add to user's bashrc or create a monitoring script
chmod 000 ~/Downloads/*.tim 2>/dev/null

# Alternative: Configure file manager to quarantine TIM files
# Create AppArmor/SELinux profile restricting GIMP's TIM loader access