CVE-2026-4887: GIMP PCX Loader DoS Vulnerability

CVE-2026-4887 Overview

A heap buffer over-read vulnerability has been discovered in GIMP's PCX file loader component. This security flaw stems from an off-by-one error in the PCX image parsing logic, allowing attackers to potentially read beyond the boundaries of allocated heap memory. A remote attacker could exploit this vulnerability by convincing a user to open a specially crafted PCX image file. Successful exploitation could lead to out-of-bounds memory disclosure and application crash, resulting in a Denial of Service (DoS) condition.

Critical Impact

This vulnerability enables out-of-bounds memory disclosure and can cause application crashes through maliciously crafted PCX image files, potentially exposing sensitive memory contents or disrupting user workflows.

Affected Products

• GIMP (GNU Image Manipulation Program) - PCX file loader component
• Linux distributions packaging vulnerable GIMP versions
• Systems with GIMP installed that process PCX image files

Discovery Timeline

• 2026-03-26 - CVE-2026-4887 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-4887

Vulnerability Analysis

This vulnerability is classified as CWE-193 (Off-by-one Error), a common programming mistake that occurs when a loop iterates one time too many or too few, or when array indexing calculations are incorrect by a single unit. In the context of GIMP's PCX file loader, this off-by-one error allows read operations to extend beyond the intended buffer boundaries during PCX image processing.

The flaw requires local access and user interaction, as an attacker must convince the victim to open a maliciously crafted PCX file. When successfully exploited, the vulnerability can lead to the disclosure of sensitive information stored in adjacent memory regions, as well as application instability resulting in crashes.

Root Cause

The root cause of CVE-2026-4887 is an off-by-one error within GIMP's PCX file parsing code. During the processing of PCX image data, a boundary calculation error causes the loader to read one byte beyond the allocated heap buffer. This type of error typically occurs in loop boundary conditions or array index calculations where the programmer incorrectly uses <= instead of <, or miscalculates the buffer size by exactly one byte.

PCX files contain image data in a specific format with run-length encoding, and the vulnerability manifests when parsing this encoded data with incorrect bounds checking.

Attack Vector

The attack vector for this vulnerability requires local access and user interaction. An attacker must craft a malicious PCX image file with specific properties designed to trigger the off-by-one error in the file loader. The attack scenario typically involves:

1. Creating a specially crafted PCX file with manipulated header values or image data
2. Distributing the malicious file through email attachments, web downloads, or shared network locations
3. Convincing the target user to open the file in GIMP
4. Upon file parsing, the vulnerable code reads one byte beyond the allocated buffer

The vulnerability manifests in the PCX file parsing logic where boundary calculations fail to properly account for buffer limits. For detailed technical information, refer to the GNOME GIMP Issue #15960 and the Red Hat Bug Report #2451669.

Detection Methods for CVE-2026-4887

Indicators of Compromise

• Unexpected GIMP application crashes when opening PCX image files
• Core dumps or crash reports indicating heap corruption in PCX loader functions
• Unusual memory access patterns in GIMP processes during PCX file operations
• Error messages or exceptions related to buffer overflows or memory access violations

Detection Strategies

• Monitor for GIMP process crashes with stack traces pointing to PCX file handling code
• Implement file integrity monitoring on systems processing untrusted PCX images
• Use AddressSanitizer (ASan) or similar memory safety tools during GIMP execution in testing environments
• Deploy endpoint detection solutions that can identify attempts to exploit memory corruption vulnerabilities

Monitoring Recommendations

• Enable crash reporting and telemetry for GIMP installations across the organization
• Implement network monitoring to detect suspicious PCX file downloads from untrusted sources
• Configure email gateway scanning to inspect PCX attachments for potential exploitation attempts
• Monitor system logs for signs of application instability related to image processing

How to Mitigate CVE-2026-4887

Immediate Actions Required

• Update GIMP to the latest patched version when available from the official GIMP project
• Exercise caution when opening PCX files from untrusted or unknown sources
• Consider temporarily disabling PCX file support if not required for business operations
• Implement application sandboxing to limit the impact of potential exploitation
• Review and restrict user permissions for installing or running unpatched software

Patch Information

Security updates addressing this vulnerability are being tracked through the official GIMP project. Users should monitor the following resources for patch availability:

• GNOME GIMP Issue #15960 - Official GIMP bug tracker
• Red Hat CVE-2026-4887 Advisory - Red Hat security advisory
• Red Hat Bug Report #2451669 - Red Hat Bugzilla tracking

Linux distribution users should apply security updates through their package managers once patches are released.

Workarounds

• Avoid opening PCX files from untrusted sources until a patch is available
• Convert PCX files to other formats (PNG, JPEG) using alternative tools before opening in GIMP
• Run GIMP in a sandboxed environment or virtual machine when working with untrusted images
• Implement strict file type filtering at email gateways and web proxies to block suspicious PCX files

# Workaround: Convert PCX files to PNG before opening in GIMP
# Using ImageMagick as an alternative converter
convert untrusted_image.pcx safe_image.png

# Or use a sandboxed environment with firejail
firejail --private gimp suspicious_file.pcx