CVE-2026-2239: GIMP Heap Buffer Overflow DoS Vulnerability

CVE-2026-2239 Overview

A heap-buffer-overflow vulnerability has been identified in GIMP (GNU Image Manipulation Program) affecting the fread_pascal_string function when processing specially crafted PSD (Photoshop Document) files. This vulnerability occurs due to improper null-termination of buffers allocated for Pascal strings, which leads to an out-of-bounds read when strlen() is subsequently called on the improperly terminated buffer. Successful exploitation of this vulnerability results in application crashes, causing a Denial of Service condition.

Critical Impact

Attackers can craft malicious PSD files that cause GIMP to crash when opened, resulting in application-level Denial of Service and potential loss of unsaved work.

Affected Products

• GIMP (GNU Image Manipulation Program) - versions with vulnerable fread_pascal_string function
• Linux distributions packaging affected GIMP versions
• Systems processing untrusted PSD files through GIMP

Discovery Timeline

• 2026-03-26 - CVE CVE-2026-2239 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-2239

Vulnerability Analysis

This vulnerability is classified as CWE-170 (Improper Null Termination). The flaw exists in the PSD file parsing code within GIMP, specifically in the fread_pascal_string function responsible for reading Pascal-style strings from Photoshop Document files.

Pascal strings differ from C strings in that they store the string length as a prefix byte rather than using null termination. When GIMP reads these Pascal strings from PSD files, the code allocates a buffer based on the length prefix but fails to ensure proper null termination of the resulting C string. When standard C library functions like strlen() are subsequently called on this buffer, they continue reading memory beyond the allocated buffer boundaries, searching for a null terminator that may not exist within the expected range.

This out-of-bounds read can access memory outside the heap allocation, causing memory access violations that result in application crashes. The vulnerability requires local access and user interaction (opening a malicious file), which limits its exploitability but still poses a risk in scenarios where users receive and open untrusted PSD files.

Root Cause

The root cause is improper null termination in the fread_pascal_string function. When converting Pascal strings (length-prefixed) to C strings (null-terminated), the code fails to append a null byte at the end of the allocated buffer. This violates the expected contract for C string functions, which assume strings are properly null-terminated. The subsequent call to strlen() then reads beyond the buffer boundary, triggering a heap-buffer-overflow read condition.

Attack Vector

Exploitation requires a local attack vector where the attacker must convince a user to open a maliciously crafted PSD file. The attacker would create a PSD file with a specially crafted Pascal string structure designed to trigger the vulnerable code path. When the victim opens this file in GIMP, the application will crash due to the out-of-bounds memory read.

The attack flow involves:

1. Creating a malformed PSD file with crafted Pascal string data
2. Distributing the malicious file to potential victims
3. Victim opens the file in GIMP
4. The fread_pascal_string function processes the malicious string
5. strlen() reads beyond buffer boundaries
6. Application crashes, causing Denial of Service

Detection Methods for CVE-2026-2239

Indicators of Compromise

• GIMP application crashes when opening specific PSD files
• Crash dumps indicating memory access violations in the PSD parsing code
• Segmentation fault logs pointing to fread_pascal_string or related functions
• Unusual PSD files with malformed Pascal string structures

Detection Strategies

• Monitor for repeated GIMP crashes during PSD file operations
• Implement file integrity checking for PSD files from untrusted sources
• Deploy application crash monitoring to detect exploitation attempts
• Use memory sanitizers (ASan/MSan) in development environments to detect similar issues

Monitoring Recommendations

• Enable core dump collection to analyze crash patterns related to PSD processing
• Monitor system logs for GIMP segmentation faults or memory violations
• Track user reports of unexpected application crashes when opening image files
• Implement endpoint detection rules for suspicious PSD file characteristics

How to Mitigate CVE-2026-2239

Immediate Actions Required

• Avoid opening PSD files from untrusted or unknown sources until patched
• Update GIMP to the latest version once a security patch is available
• Use alternative image editors for processing untrusted PSD files
• Educate users about the risks of opening files from unknown sources

Patch Information

Users should monitor the official GIMP security channels and update to the patched version when available. Additional information can be found through the following resources:

• Red Hat CVE-2026-2239 Advisory
• Red Hat Bug Report #2437675
• GNOME GIMP Issue #15812

Workarounds

• Do not open PSD files from untrusted sources
• Convert PSD files to safer formats (PNG, JPEG) using other tools before editing
• Run GIMP in a sandboxed environment when processing untrusted files
• Consider using GIMP's command-line export capabilities with resource limits for batch processing untrusted files

# Configuration example - Run GIMP in sandbox (using Flatpak or firejail)
# Using firejail to sandbox GIMP
firejail --seccomp --private-tmp gimp-2.10

# Or use Flatpak's built-in sandboxing
flatpak run org.gimp.GIMP