CVE-2026-25898: ImageMagick Buffer Overflow Vulnerability

CVE-2026-25898 Overview

A critical out-of-bounds read vulnerability has been discovered in ImageMagick, a widely-used open-source software suite for image editing and manipulation. The vulnerability exists in the UIL and XPM image encoders, which fail to validate pixel index values returned by the GetPixelIndex() function before using them as array subscripts.

In HDRI (High Dynamic Range Imaging) builds of ImageMagick, the Quantum data type is implemented as a floating-point number, allowing pixel index values to be negative. An attacker can craft a malicious image containing negative pixel index values to trigger a global buffer overflow read during image conversion operations. This can result in information disclosure through leaked memory contents or cause the ImageMagick process to crash.

Critical Impact

Remote attackers can exploit this vulnerability to read sensitive memory contents or crash ImageMagick processes by supplying specially crafted images to any application using vulnerable ImageMagick versions for image conversion.

Affected Products

• ImageMagick versions prior to 7.1.2-15
• ImageMagick versions prior to 6.9.13-40
• Applications and services utilizing ImageMagick HDRI builds for image processing

Discovery Timeline

• 2026-02-24 - CVE-2026-25898 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-25898

Vulnerability Analysis

The vulnerability stems from insufficient input validation within ImageMagick's UIL (User Interface Language) and XPM (X PixMap) image encoders. When processing image data, these encoders call the GetPixelIndex() function to retrieve pixel index values. However, the returned values are used directly as array subscripts without proper bounds checking.

In standard ImageMagick builds, the Quantum type is typically an unsigned integer, which naturally prevents negative values. However, HDRI builds configure Quantum as a floating-point type to support high dynamic range color values. This floating-point representation allows for negative values, which the code paths in the UIL and XPM encoders do not anticipate or handle.

When a negative pixel index is used as an array subscript, it causes the program to read memory locations before the intended array buffer. This out-of-bounds read can expose sensitive information from the process's memory space or cause an access violation leading to a crash.

Root Cause

The root cause is improper input validation in the UIL and XPM encoder code paths. The GetPixelIndex() function can return negative floating-point values in HDRI builds, but the encoder logic assumes non-negative integer-like behavior. The absence of bounds checking before array indexing creates a classic CWE-125 (Out-of-bounds Read) vulnerability.

Attack Vector

The attack is network-based and requires no privileges or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious image file with specially constructed pixel data that results in negative index values when processed by GetPixelIndex()
2. Submitting this image to any web application, service, or system that uses a vulnerable HDRI build of ImageMagick for image conversion
3. When ImageMagick processes the image through the UIL or XPM encoder, the negative indices cause out-of-bounds memory reads

The vulnerability mechanism involves the GetPixelIndex() function returning floating-point values that can be negative in HDRI builds. When these values are cast or used as array indices without validation, memory before the array's base address is accessed. Technical details regarding the specific encoding routines and patch implementation are available in the GitHub Security Advisory.

Detection Methods for CVE-2026-25898

Indicators of Compromise

• Unexpected ImageMagick process crashes during image conversion operations, particularly involving UIL or XPM format output
• Memory access violations or segmentation faults in ImageMagick-related processes
• Unusual image files with malformed pixel data being submitted to image processing endpoints
• Error logs indicating buffer read errors or memory corruption in ImageMagick components

Detection Strategies

• Monitor ImageMagick processes for abnormal termination signals (SIGSEGV, SIGBUS) that may indicate exploitation attempts
• Implement file integrity monitoring on ImageMagick binaries to detect unauthorized modifications
• Deploy endpoint detection rules to identify suspicious image files being processed through ImageMagick pipelines
• Analyze application logs for repeated failed image conversion attempts that could indicate probing activity

Monitoring Recommendations

• Enable verbose logging for ImageMagick operations to capture detailed error information
• Implement anomaly detection for image processing services to identify unusual patterns in file submissions
• Monitor network traffic for bulk uploads of potentially malicious image files to processing endpoints
• Configure alerting for repeated crashes or memory errors in image processing infrastructure

How to Mitigate CVE-2026-25898

Immediate Actions Required

• Upgrade ImageMagick to version 7.1.2-15 or later for the 7.x branch
• Upgrade ImageMagick to version 6.9.13-40 or later for the 6.x branch
• If immediate patching is not possible, consider temporarily disabling UIL and XPM encoder support in ImageMagick policy files
• Audit systems and applications to identify all instances of ImageMagick HDRI builds that require patching

Patch Information

ImageMagick has released patched versions that add proper validation of pixel index values before use as array subscripts. The fix ensures bounds checking is performed on values returned by GetPixelIndex() to prevent negative indices from being used.

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

Full details about the vulnerability and patch are available in the GitHub Security Advisory.

Workarounds

• Disable UIL and XPM coders in the ImageMagick policy.xml configuration file until patching is complete
• Implement input validation to reject potentially malicious image files before they reach ImageMagick
• Run ImageMagick processes in sandboxed environments with restricted memory access and resource limits
• Consider using non-HDRI builds of ImageMagick where high dynamic range support is not required

# Disable UIL and XPM coders in ImageMagick policy.xml
# Add these lines to /etc/ImageMagick-7/policy.xml (or appropriate path)
<policy domain="coder" rights="none" pattern="UIL" />
<policy domain="coder" rights="none" pattern="XPM" />