CVE-2026-25796: ImageMagick Memory Leak DoS Vulnerability

CVE-2026-25796 Overview

CVE-2026-25796 is a memory leak vulnerability in ImageMagick, the widely-used open-source software for editing and manipulating digital images. The vulnerability exists in the ReadSTEGANOImage() function within coders/stegano.c, where the watermark Image object is not properly freed on three early-return paths. This results in a memory leak of approximately 13.5KB or more per invocation, which can be exploited by attackers to cause denial of service conditions through resource exhaustion.

Critical Impact

Attackers can exploit this memory leak vulnerability to exhaust system memory resources by triggering repeated processing of malicious STEGANO image files, leading to denial of service conditions affecting application availability.

Affected Products

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

Discovery Timeline

• 2026-02-24 - CVE CVE-2026-25796 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2026-25796

Vulnerability Analysis

This vulnerability is classified as CWE-401 (Missing Release of Memory after Effective Lifetime). The flaw resides in ImageMagick's STEGANO image codec, specifically within the ReadSTEGANOImage() function located in coders/stegano.c. When processing STEGANO image files, the function allocates memory for a watermark Image object. However, on three distinct early-return code paths where the function exits prematurely due to error conditions, this allocated memory is not properly deallocated.

Each invocation that triggers one of these vulnerable code paths leaks approximately 13.5KB or more of memory. While this may seem modest for a single request, repeated exploitation can rapidly consume available system memory. In server environments where ImageMagick processes user-supplied images, an attacker can submit numerous malicious requests to systematically exhaust memory resources.

The vulnerability is exploitable over the network without requiring authentication or user interaction, making it particularly concerning for web applications and services that use ImageMagick for image processing.

Root Cause

The root cause is improper resource management in the ReadSTEGANOImage() function. When the function allocates memory for the watermark Image object and subsequently encounters an error condition that triggers an early return, the developer failed to include the necessary cleanup code to free the allocated watermark object before exiting. This oversight occurs on three separate early-return paths within the function, each of which should include a call to destroy the watermark Image object to prevent the memory leak.

Attack Vector

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

1. Crafting or submitting STEGANO image files designed to trigger the vulnerable early-return code paths in ReadSTEGANOImage()
2. Repeatedly sending these malicious images to a server or application that processes images using vulnerable ImageMagick versions
3. Each request leaks ~13.5KB+ of memory that is never reclaimed
4. Sustained attack traffic causes memory exhaustion, degraded performance, and eventual denial of service

The vulnerability mechanism involves triggering error conditions in the STEGANO image processing logic that cause premature function returns. When these error paths are taken, the allocated watermark Image object remains in memory without being freed. For detailed technical analysis, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-25796

Indicators of Compromise

• Unusual increase in STEGANO image file processing requests or errors
• Gradual memory consumption growth in ImageMagick processes without corresponding workload increase
• Application or service crashes due to out-of-memory conditions
• System logs showing memory allocation failures in image processing components

Detection Strategies

• Monitor memory usage patterns of processes utilizing ImageMagick libraries for abnormal growth trends
• Implement rate limiting and logging for image processing endpoints to detect potential exploitation attempts
• Use application performance monitoring to track memory allocation in image codec operations
• Configure alerting for sustained memory growth in ImageMagick-dependent services

Monitoring Recommendations

• Set up memory usage thresholds and alerts for ImageMagick processes
• Log and analyze image processing errors, particularly those related to STEGANO format handling
• Monitor for repeated failed or error-inducing image processing requests from single sources
• Track system-wide memory availability and set proactive alerts before critical thresholds

How to Mitigate CVE-2026-25796

Immediate Actions Required

• Update ImageMagick to version 7.1.2-15 or later (for 7.x branch)
• Update ImageMagick to version 6.9.13-40 or later (for 6.x branch)
• If immediate patching is not possible, consider disabling STEGANO coder support
• Implement rate limiting on image processing endpoints to reduce exploitation impact

Patch Information

ImageMagick has released patches addressing this vulnerability in versions 7.1.2-15 and 6.9.13-40. The fix ensures proper deallocation of the watermark Image object on all early-return paths within the ReadSTEGANOImage() function. Organizations should prioritize upgrading to these patched versions. Refer to the ImageMagick Security Advisory for complete details.

Workarounds

• Disable the STEGANO coder in ImageMagick's policy configuration if not required
• Implement strict input validation to reject or quarantine STEGANO format images
• Configure memory limits for ImageMagick processes to contain potential exploitation impact
• Deploy request rate limiting for image processing services to slow exploitation attempts

# Configuration example - Disable STEGANO coder in ImageMagick policy.xml
# Add the following line to /etc/ImageMagick-7/policy.xml or equivalent
<policy domain="coder" rights="none" pattern="STEGANO" />

# Set memory limits for ImageMagick processes
<policy domain="resource" name="memory" value="256MiB"/>
<policy domain="resource" name="map" value="512MiB"/>