CVE-2026-40915: GIMP FITS Loader DoS Vulnerability

CVE-2026-40915 Overview

A flaw was found in GIMP where a remote attacker could exploit an integer overflow vulnerability in the FITS image loader by providing a specially crafted FITS file. This integer overflow leads to a zero-byte memory allocation, which is then subjected to a heap buffer overflow when processing pixel data. Successful exploitation could result in a denial of service (DoS) or potentially arbitrary code execution.

Critical Impact

Integer overflow in GIMP's FITS image loader can cause zero-byte memory allocation followed by heap buffer overflow, potentially enabling arbitrary code execution when users open malicious FITS files.

Affected Products

• GIMP (GNU Image Manipulation Program)
• Systems with FITS image file support enabled in GIMP

Discovery Timeline

• 2026-04-15 - CVE-2026-40915 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2026-40915

Vulnerability Analysis

This vulnerability (CWE-190: Integer Overflow or Wraparound) affects the FITS (Flexible Image Transport System) image loader component in GIMP. FITS is a standard digital file format used mainly in astronomy to store images and data tables. When GIMP processes a specially crafted FITS file, the integer overflow occurs during image dimension calculations, resulting in a zero-byte or undersized memory allocation. Subsequently, when pixel data is written to this insufficient buffer, a heap buffer overflow occurs.

The local attack vector requires user interaction—specifically, the victim must open a malicious FITS file. While the attack complexity is low, successful exploitation depends on social engineering to convince a user to open the attacker-controlled file. The primary impact is on availability (denial of service through application crash), though arbitrary code execution may be possible in certain conditions.

Root Cause

The root cause lies in improper handling of integer arithmetic when calculating buffer sizes for FITS image data. When image dimensions are parsed from a malicious FITS file header, the multiplication of width, height, and color depth values can overflow the integer type used for the calculation. This results in a much smaller allocation than required—potentially zero bytes—while the actual pixel data writing operation uses the original (large) dimensions.

Attack Vector

An attacker crafts a malicious FITS file with specially chosen image dimension values that cause an integer overflow during buffer size calculation. When a user opens this file in GIMP:

1. GIMP parses the FITS header and extracts image dimensions
2. Buffer size is calculated by multiplying dimensions, causing integer overflow
3. A zero-byte or undersized buffer is allocated
4. Pixel data is written to the buffer using original dimensions
5. Heap buffer overflow occurs, corrupting adjacent memory
6. Application crashes (DoS) or potentially executes attacker-controlled code

The vulnerability is exploited locally, requiring the victim to open the malicious file. No network-based exploitation vector exists without user interaction.

Detection Methods for CVE-2026-40915

Indicators of Compromise

• Unexpected GIMP application crashes when opening FITS files
• FITS files with anomalously large or suspicious dimension values in headers
• Memory access violations or segmentation faults in GIMP processes
• Presence of .fits or .fit files from untrusted sources in user directories

Detection Strategies

• Monitor for GIMP process crashes, particularly when processing FITS format files
• Implement file validation to detect FITS files with dimension values that could cause integer overflow
• Deploy endpoint detection rules to identify suspicious file handling patterns in image editing applications
• Use memory corruption detection tools to identify heap overflow conditions

Monitoring Recommendations

• Enable application crash reporting to identify potential exploitation attempts
• Monitor user download directories for FITS files from untrusted sources
• Implement logging for file open operations in GIMP to track suspicious activity
• Consider blocking or quarantining FITS files from external sources pending validation

How to Mitigate CVE-2026-40915

Immediate Actions Required

• Avoid opening FITS files from untrusted or unknown sources
• Update GIMP to the latest patched version when security updates become available
• Review and restrict file type associations for FITS files if not required for business operations
• Educate users about the risks of opening image files from untrusted sources

Patch Information

No official patch information is available at this time. Monitor the Red Hat CVE-2026-40915 Advisory and Red Hat Bugzilla Report #2458744 for updates on patch availability from your distribution or the upstream GIMP project.

Workarounds

• Disable or remove FITS file format support in GIMP if not required
• Use sandboxing solutions (such as Flatpak, Snap, or containerization) to isolate GIMP from critical system resources
• Implement strict file filtering at the perimeter to block FITS files from external sources
• Configure systems to require elevated permissions before opening FITS files

Until an official patch is available, the safest approach is to avoid processing FITS files from untrusted sources. For organizations that require FITS file handling, running GIMP in an isolated environment or virtual machine provides an additional layer of protection against potential exploitation.