CVE-2026-25970: ImageMagick SIXEL Decoder DoS Vulnerability

CVE-2026-25970 Overview

A signed integer overflow vulnerability exists in ImageMagick's SIXEL decoder that allows attackers to trigger memory corruption and denial of service when processing maliciously crafted SIXEL image files. ImageMagick is widely-used free and open-source software for editing and manipulating digital images, making this vulnerability particularly impactful for systems that process user-supplied images.

Critical Impact

Processing a maliciously crafted SIXEL image file can trigger memory corruption and denial of service, potentially disrupting critical image processing workflows and services.

Affected Products

• ImageMagick versions prior to 7.1.2-15
• ImageMagick versions prior to 6.9.13-40

Discovery Timeline

• 2026-02-24 - CVE-2026-25970 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-25970

Vulnerability Analysis

This vulnerability is classified as an Integer Overflow (CWE-190) affecting the SIXEL decoder component in ImageMagick. The flaw occurs during buffer reallocation operations where pointer arithmetic using signed 32-bit integers can overflow beyond their maximum representable value.

SIXEL (DEC Sixel Graphics) is a bitmap graphics format that allows images to be transmitted to supported terminals. When ImageMagick parses SIXEL image data, it dynamically allocates and reallocates memory buffers to store the decoded image data. The vulnerable code path performs arithmetic operations on buffer sizes and offsets using signed 32-bit integers without adequate bounds checking.

When an attacker supplies specially crafted SIXEL image dimensions or color data that causes these integer values to wrap around, the resulting buffer operations can lead to memory corruption. This manifests as either writing to unintended memory locations or reading from out-of-bounds areas, ultimately resulting in application crashes and denial of service conditions.

Root Cause

The root cause is improper handling of integer arithmetic in the SIXEL decoder's buffer reallocation logic. When processing SIXEL image data, the decoder uses signed 32-bit integers for pointer arithmetic and size calculations. Without proper validation, these values can overflow when processing malicious input, causing the allocated buffer size to be smaller than expected or causing pointer arithmetic to produce invalid memory addresses.

Attack Vector

The attack can be conducted remotely over a network without requiring authentication or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious SIXEL image file with dimensions or color data designed to trigger the integer overflow
2. Delivering the malicious file to a target system through various channels (web upload, email attachment, file sharing)
3. When ImageMagick processes the file, the overflow occurs during buffer reallocation
4. The memory corruption results in application crash and denial of service

The vulnerability is particularly dangerous in environments where ImageMagick automatically processes uploaded images, such as web applications with image upload functionality, content management systems, or image processing pipelines.

Detection Methods for CVE-2026-25970

Indicators of Compromise

• Unexpected ImageMagick process crashes when processing SIXEL format images
• Segmentation faults or memory corruption errors in application logs related to ImageMagick
• Abnormal memory allocation patterns during image processing operations
• Repeated service restarts or unavailability of image processing functionality

Detection Strategies

• Monitor for process crashes and core dumps associated with ImageMagick binaries (convert, identify, mogrify, magick)
• Implement file type validation to identify and log SIXEL image uploads before processing
• Deploy application-level monitoring for abnormal resource consumption during image operations
• Review system logs for repeated failures in image processing workflows

Monitoring Recommendations

• Enable detailed logging for ImageMagick operations to capture processing failures
• Set up alerts for ImageMagick process termination signals indicating crashes (SIGSEGV, SIGABRT)
• Monitor system resource metrics for unusual memory patterns during image processing
• Implement file upload scanning to identify potentially malicious SIXEL images before processing

How to Mitigate CVE-2026-25970

Immediate Actions Required

• Upgrade ImageMagick to version 7.1.2-15 or later (for 7.x branch) immediately
• Upgrade ImageMagick to version 6.9.13-40 or later (for 6.x branch) if using the legacy version
• Review and restrict the image formats allowed for processing using ImageMagick policy configuration
• Implement input validation to reject or quarantine suspicious SIXEL files

Patch Information

The ImageMagick development team has released patched versions that address this integer overflow vulnerability. Organizations should upgrade to the following versions:

• ImageMagick 7.x: Upgrade to version 7.1.2-15 or later
• ImageMagick 6.x: Upgrade to version 6.9.13-40 or later

For additional details, refer to the GitHub Security Advisory.

Workarounds

• Disable SIXEL decoder support in ImageMagick policy configuration until patches can be applied
• Implement strict file type filtering to block SIXEL format images at the application layer
• Process images in sandboxed environments with restricted permissions to limit impact of exploitation
• Use containerization or process isolation for ImageMagick operations to contain potential crashes

If upgrading is not immediately possible, the SIXEL decoder can be disabled by modifying the ImageMagick policy configuration file (policy.xml):

<!-- Disable SIXEL decoder to mitigate CVE-2026-25970 -->
<policy domain="coder" rights="none" pattern="SIXEL" />