CVE-2023-39978: ImageMagick DOS Vulnerability

CVE-2023-39978 Overview

CVE-2023-39978 is a memory leak vulnerability in ImageMagick before version 6.9.12-91 that allows attackers to cause a denial of service through excessive memory consumption. The vulnerability exists in the Magick::Draw component, where improper memory management can lead to resource exhaustion when processing specially crafted image operations.

Critical Impact

Attackers can exploit this vulnerability to exhaust system memory resources, potentially causing application crashes and denial of service conditions on systems processing untrusted image content.

Affected Products

• ImageMagick versions prior to 6.9.12-91
• Fedora 37 (via bundled ImageMagick packages)
• Applications using RMagick bindings that depend on vulnerable ImageMagick versions

Discovery Timeline

• 2023-08-08 - CVE-2023-39978 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-39978

Vulnerability Analysis

This vulnerability is classified as CWE-401 (Missing Release of Memory after Effective Lifetime), commonly known as a memory leak. The flaw resides in the CloneDrawInfo() function within ImageMagick's magick/draw.c source file. When draw information structures are cloned during image processing operations, the function improperly allocated and copied image info data without proper memory management, leading to memory that is never released.

The vulnerability requires local access and user interaction to exploit, as an attacker would need to convince a user to process a maliciously crafted image or execute drawing operations that trigger repeated cloning of draw info structures. Over time, repeated exploitation can exhaust available system memory.

Root Cause

The root cause of this vulnerability lies in the CloneDrawInfo() function's handling of the image_info member. The vulnerable code unnecessarily called CloneImageInfo(draw_info->image_info) when creating a clone of draw information, which allocated new memory for the image info structure. This memory was not properly tracked or released, resulting in a memory leak each time the function was called.

Attack Vector

The attack vector requires local access with user interaction. An attacker can exploit this vulnerability by:

1. Crafting image files or scripts that trigger repeated Magick::Draw operations
2. Convincing a user or application to process these files
3. Causing the vulnerable CloneDrawInfo() function to be called repeatedly
4. Gradually exhausting system memory resources leading to denial of service

The following patch shows how the vulnerability was fixed by removing the problematic memory allocation:

     clone_info->composite_mask=CloneImage(draw_info->composite_mask,0,0,
       MagickTrue,&draw_info->composite_mask->exception);
     clone_info->render=draw_info->render;
-  clone_info->image_info=CloneImageInfo(draw_info->image_info);
   clone_info->debug=draw_info->debug;
   return(clone_info);
 }

Source: ImageMagick6 GitHub Commit

Detection Methods for CVE-2023-39978

Indicators of Compromise

• Unusually high memory consumption by ImageMagick processes or applications using ImageMagick libraries
• System memory exhaustion events coinciding with image processing operations
• Application crashes or out-of-memory errors when processing image files with draw operations
• Gradual memory growth in long-running services utilizing ImageMagick

Detection Strategies

• Monitor memory utilization of processes using ImageMagick libraries for abnormal growth patterns
• Implement process memory limits to prevent runaway memory consumption from affecting system stability
• Use version scanning tools to identify systems running ImageMagick versions prior to 6.9.12-91
• Review application logs for out-of-memory exceptions related to image processing

Monitoring Recommendations

• Configure memory usage alerts for applications that process untrusted image content
• Implement resource quotas and cgroups to limit memory consumption of image processing services
• Deploy endpoint detection and response (EDR) solutions to monitor for unusual resource consumption patterns
• Regularly audit installed ImageMagick versions across your environment

How to Mitigate CVE-2023-39978

Immediate Actions Required

• Upgrade ImageMagick to version 6.9.12-91 or later to receive the official security fix
• Apply available security updates from your Linux distribution's package manager
• For Fedora 37 systems, apply the security update referenced in the Fedora Package Announcement
• Review and update RMagick bindings if using Ruby applications with ImageMagick

Patch Information

The vulnerability was fixed in ImageMagick version 6.9.12-91. The patch removes the unnecessary CloneImageInfo() call in the CloneDrawInfo() function that was causing the memory leak. Organizations should upgrade to this version or later. The fix can be reviewed in the GitHub Version Comparison between versions 6.9.12-90 and 6.9.12-91.

Workarounds

• Implement memory limits using system resource controls (ulimit, cgroups) for processes running ImageMagick
• Restrict processing of untrusted image content to isolated sandbox environments
• Configure periodic restart of long-running ImageMagick-based services to reclaim leaked memory
• Disable or limit draw operations in ImageMagick policy.xml configuration if not required

# Configuration example - Set memory limits for ImageMagick processes
# Add to /etc/ImageMagick-6/policy.xml or /etc/ImageMagick/policy.xml
# Limit memory usage to prevent DoS from memory leaks
<policy domain="resource" name="memory" value="256MiB"/>
<policy domain="resource" name="map" value="512MiB"/>
<policy domain="resource" name="disk" value="1GiB"/>