CVE-2026-25794: ImageMagick Buffer Overflow Vulnerability

CVE-2026-25794 Overview

CVE-2026-25794 is an integer overflow vulnerability in ImageMagick, the widely-used open-source software for editing and manipulating digital images. The vulnerability exists in the WriteUHDRImage function within coders/uhdr.c, where integer arithmetic is used to compute the pixel buffer size. When processing images with large dimensions, the multiplication operation overflows the 32-bit int data type, resulting in an undersized heap allocation followed by an out-of-bounds write.

Critical Impact

This vulnerability can crash the ImageMagick process or potentially allow attackers to achieve an out-of-bounds heap write through specially crafted images with large dimensions, impacting systems that process untrusted image files.

Affected Products

• ImageMagick versions prior to 7.1.2-15
• Systems processing UHDR image formats with ImageMagick
• Web applications and services using ImageMagick for image processing

Discovery Timeline

• 2026-02-24 - CVE-2026-25794 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2026-25794

Vulnerability Analysis

The vulnerability stems from improper integer handling in the WriteUHDRImage function located in coders/uhdr.c. When ImageMagick processes an image for UHDR output, it calculates the required buffer size by multiplying the image dimensions. This calculation uses 32-bit signed integer (int) arithmetic, which has a maximum value of approximately 2.1 billion.

When an attacker supplies an image with carefully chosen large dimensions, the multiplication of width × height × bytes-per-pixel can exceed this limit, causing the integer to wrap around to a small or negative value. This results in a heap allocation that is significantly smaller than required to hold the actual pixel data.

As ImageMagick proceeds to write pixel data into this undersized buffer, it performs an out-of-bounds heap write, potentially corrupting adjacent memory structures. This memory corruption can lead to application crashes (denial of service) or, in more severe scenarios, could potentially be leveraged for code execution if an attacker can control the overwritten memory contents.

Root Cause

The root cause is the use of 32-bit signed integer arithmetic for buffer size calculations without proper overflow checking. The WriteUHDRImage function computes the pixel buffer size using int data types, which cannot safely represent the product of large image dimensions. Prior to the patch in version 7.1.2-15, no validation was performed to detect when this calculation would overflow, leading to heap buffer allocation errors.

Attack Vector

The vulnerability can be exploited remotely over a network by convincing a target system to process a malicious image file. The attack vector involves:

1. An attacker crafts a malicious image file with extremely large dimension values specified in the image headers
2. The malicious file is submitted to a system running a vulnerable version of ImageMagick (such as a web application that processes user uploads)
3. When ImageMagick attempts to write the image in UHDR format, the integer overflow occurs during buffer size calculation
4. The undersized buffer allocation leads to heap corruption when pixel data is written

The vulnerability is particularly dangerous for web services, content management systems, and any automated image processing pipelines that handle untrusted image inputs using ImageMagick.

Detection Methods for CVE-2026-25794

Indicators of Compromise

• Unexpected crashes or segmentation faults in ImageMagick or applications using the ImageMagick library
• Core dumps containing evidence of heap corruption near UHDR processing functions
• Abnormal image files with unusually large dimension values in their headers
• Log entries showing failed image conversions with memory allocation errors

Detection Strategies

• Monitor for process crashes related to ImageMagick binaries (convert, magick, mogrify) with heap corruption signatures
• Implement input validation to reject images with dimensions exceeding safe thresholds before passing to ImageMagick
• Deploy runtime memory protection tools (ASAN, Valgrind) in testing environments to detect out-of-bounds writes
• Use file integrity monitoring to detect unexpected changes to ImageMagick configuration or policy files

Monitoring Recommendations

• Enable verbose logging for ImageMagick operations to capture processing errors and dimension information
• Implement alerting on repeated ImageMagick process restarts or crashes within short time windows
• Monitor resource consumption patterns for image processing services that may indicate exploitation attempts
• Review and audit image upload logs for files with suspicious or extreme dimension metadata

How to Mitigate CVE-2026-25794

Immediate Actions Required

• Upgrade ImageMagick to version 7.1.2-15 or later immediately
• If immediate upgrade is not possible, disable UHDR coder by adding policy restrictions in policy.xml
• Implement input validation to limit maximum image dimensions before processing
• Review and restrict ImageMagick policy settings to limit resource consumption and disable unnecessary coders

Patch Information

ImageMagick version 7.1.2-15 contains the official fix for this vulnerability. The patch addresses the integer overflow by implementing proper bounds checking on dimension calculations before buffer allocation. Organizations should update to this version or later to remediate the vulnerability. Additional details are available in the ImageMagick Security Advisory.

Workarounds

• Add policy restrictions to disable the UHDR coder in ImageMagick's policy.xml configuration file
• Implement dimension limits using the policy.xml file to prevent processing of excessively large images
• Use application-level validation to reject images exceeding safe dimension thresholds before they reach ImageMagick
• Consider sandboxing ImageMagick processes using containers or seccomp profiles to limit potential impact

# ImageMagick policy.xml configuration to disable UHDR coder and limit dimensions
# Add these lines to /etc/ImageMagick-7/policy.xml or equivalent

# Disable UHDR coder as a workaround
# <policy domain="coder" rights="none" pattern="UHDR" />

# Limit maximum image dimensions to prevent integer overflow
# <policy domain="resource" name="width" value="16KP" />
# <policy domain="resource" name="height" value="16KP" />