CVE-2026-40917: GIMP Information Disclosure Vulnerability

CVE-2026-40917 Overview

A heap buffer over-read vulnerability was discovered in GIMP, the popular open-source image editing software. The flaw exists in the icns_slurp() function, which is responsible for processing Apple Icon Image (ICNS) files. When GIMP processes a specially crafted ICNS image file, the vulnerable function fails to properly validate buffer boundaries, leading to an out-of-bounds read condition that can result in application crashes or potential information disclosure.

Critical Impact

Attackers can craft malicious ICNS files that, when opened in GIMP, trigger a heap buffer over-read condition potentially causing denial of service through application crashes or leaking sensitive memory contents.

Affected Products

• GIMP (GNU Image Manipulation Program) - versions with vulnerable icns_slurp() implementation
• Systems processing untrusted ICNS image files through GIMP

Discovery Timeline

• April 15, 2026 - CVE-2026-40917 published to NVD
• April 15, 2026 - Last updated in NVD database

Technical Details for CVE-2026-40917

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read), a memory safety issue where the application reads data beyond the allocated buffer boundaries. The icns_slurp() function in GIMP's ICNS file parser does not adequately validate the size parameters within ICNS file structures before reading image data into memory.

When processing ICNS files, the parser trusts length fields embedded in the file format without proper bounds checking. An attacker can manipulate these length fields to cause the function to read beyond the allocated heap buffer, potentially accessing adjacent memory regions. This type of vulnerability requires local access and user interaction—the victim must open the malicious file with GIMP.

The attack scenario involves social engineering to convince a user to open a crafted ICNS file, or placing malicious files in locations where they might be automatically processed or previewed. The impact is primarily availability-focused, as the over-read condition typically leads to application crashes when accessing invalid memory regions.

Root Cause

The root cause lies in insufficient input validation within the icns_slurp() function. The ICNS file format contains multiple icon resources with their own size descriptors. The vulnerable code path reads these size values and uses them to determine how much data to copy from the file into memory buffers. Without proper validation that these sizes are within expected bounds and don't exceed allocated buffer sizes, the function proceeds to read beyond buffer boundaries when processing malformed files.

Attack Vector

The attack requires local access with low privileges and user interaction (opening a malicious file). An attacker would:

1. Craft a malicious ICNS file with manipulated size fields that exceed actual data boundaries
2. Distribute the file through phishing, file sharing, or by embedding it in seemingly legitimate project archives
3. Wait for a victim to open the file in GIMP, triggering the heap buffer over-read
4. The over-read causes the application to crash or potentially leak memory contents from adjacent heap allocations

The vulnerability mechanism involves malformed ICNS icon resource entries where the declared size exceeds the actual available data. When icns_slurp() processes these entries, it attempts to read the declared number of bytes without verifying the data actually exists, causing an out-of-bounds heap read. For detailed technical information, refer to the Red Hat Bug Report #2458746.

Detection Methods for CVE-2026-40917

Indicators of Compromise

• Unexpected GIMP crashes when opening ICNS files from untrusted sources
• Abnormal memory access patterns or segmentation faults in GIMP process logs
• Presence of unusually structured ICNS files with mismatched size headers
• Core dumps indicating heap corruption or out-of-bounds memory access in GIMP

Detection Strategies

• Monitor for GIMP process crashes associated with ICNS file operations
• Implement file integrity monitoring on systems processing image files from external sources
• Deploy memory protection tools (ASAN, Valgrind) in development/testing environments to detect out-of-bounds reads
• Use endpoint detection and response (EDR) solutions to identify suspicious crash patterns

Monitoring Recommendations

• Enable crash reporting and logging for GIMP processes across managed endpoints
• Monitor file access patterns for unusual ICNS file processing activity
• Implement alerting for repeated GIMP crashes within short time windows
• Review system logs for segmentation fault signals originating from GIMP processes

How to Mitigate CVE-2026-40917

Immediate Actions Required

• Avoid opening ICNS files from untrusted or unknown sources until a patch is available
• Disable automatic file previews for ICNS files in file managers where possible
• Implement network-level filtering to quarantine suspicious ICNS files
• Update GIMP to the latest available version and monitor for security patches

Patch Information

Consult the Red Hat CVE-2026-40917 Advisory for the latest patch status and updates. Users should apply vendor-provided updates as soon as they become available. The fix likely involves adding proper bounds checking in the icns_slurp() function to validate size parameters before performing read operations.

Workarounds

• Convert ICNS files using alternative tools before opening in GIMP to sanitize potentially malicious content
• Run GIMP in a sandboxed environment (container, VM, or application sandbox) when processing untrusted files
• Implement organizational policies restricting ICNS file handling to trusted sources only
• Use file inspection tools to validate ICNS file structure before processing

# Configuration example - Run GIMP in a sandboxed environment using Firejail
firejail --private --net=none gimp suspicious_file.icns

# Alternatively, use Flatpak's built-in sandboxing
flatpak run --filesystem=~/Downloads:ro org.gimp.GIMP