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:

1. Creating a TIM file with manipulated header fields specifying large or malformed dimensions
2. Embedding pixel data designed to overflow the stack buffer during decoding
3. Delivering the malicious file to a victim through social engineering
4. 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

# 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