CVE-2026-25798: 
C# vulnerability analysis and mitigation

CVE-2026-25798 is a NULL Pointer Dereference vulnerability in ImageMagick's ClonePixelCacheRepository function that allows a remote, unauthenticated attacker to crash any application linked against the library by supplying a crafted image file, resulting in denial of service. It affects ImageMagick versions prior to 6.9.13-40 (6.x branch) and prior to 7.1.2-15 (7.x branch), as well as Magick.NET NuGet packages prior to version 14.10.3. The vulnerability was published on February 23–24, 2026, and was reported by researcher ylwango613. The CVSS v3.1 base score is 5.3 (Medium) per the GitHub Security Advisory, though some sources (e.g., Feedly/NVD) assign a score of 7.5 (High) (Github Advisory, ImageMagick Advisory).

The root cause is a NULL pointer dereference (CWE-476) in the ClonePixelCacheRepository function within MagickCore/cache.c. When processing a specially crafted image file, the function dereferences a NULL pointer during pixel cache cloning operations, triggering an unhandled signal (SIGSEGV/UNKNOWN SIGNAL) that crashes the process. The crash stack trace shows the fault originates in the OpenMP parallel region of ClonePixelCacheRepository (cache.c:784), propagating through OpenPixelCache, GetImagePixelCache, SyncImagePixelCache, and ultimately SetImageExtent. No authentication or user interaction is required — an attacker only needs to supply a malformed image to any network-accessible service that processes images using ImageMagick (ImageMagick Advisory, Github Advisory).

Successful exploitation results in a denial of service by crashing the application process linked against vulnerable ImageMagick versions. There is no impact on confidentiality or data integrity — the vulnerability is limited to availability. Any service that accepts user-supplied image files and processes them with ImageMagick (e.g., web applications, image conversion APIs, content management systems) is at risk of being remotely crashed, potentially causing service outages (ImageMagick Advisory, Red Hat Bugzilla).

1. Reconnaissance: Identify network-accessible services that accept image uploads or process user-supplied image files using ImageMagick (e.g., web applications with image upload features, thumbnail generators, document converters). Confirm the target is running a vulnerable version (ImageMagick < 6.9.13-40 or < 7.1.2-15).
2. Craft malicious image: Create or obtain a specially crafted image file designed to trigger the NULL pointer dereference in ClonePixelCacheRepository. The crafted file must cause the pixel cache cloning logic to encounter a NULL pointer during parallel processing.
3. Submit crafted image: Upload or submit the malicious image file to the target service via its normal image intake mechanism (e.g., HTTP file upload, API endpoint, email attachment processing).
4. Trigger crash: When the application processes the image, ClonePixelCacheRepository dereferences the NULL pointer, causing an UNKNOWN SIGNAL/SIGSEGV that terminates the process, resulting in denial of service for the affected application (ImageMagick Advisory).

• Logs: Application crash logs or core dumps referencing ClonePixelCacheRepository in MagickCore/cache.c (lines 753–784); AddressSanitizer output showing DEADLYSIGNAL / UNKNOWN SIGNAL on unknown address 0x000000000000.
• Process: Unexpected termination of image-processing worker processes; repeated process restarts by a supervisor (e.g., systemd, supervisord) for services that handle image uploads.
• Network: Repeated submission of the same or similar image files to an image-processing endpoint, particularly files with unusual or malformed headers; high rate of failed image processing requests from a single source IP.
• File System: Presence of unexpected or malformed image files (e.g., zero-byte or structurally invalid files) in upload or temporary directories associated with the image-processing service (ImageMagick Advisory).

Upgrade ImageMagick to version 7.1.2-15 or later (7.x branch) or 6.9.13-40 or later (6.x branch). For Magick.NET users, upgrade to version 14.10.3 or later. Linux distribution users should apply vendor-provided security updates (patches have been issued for Debian, Ubuntu USN-8127-1, SUSE, openSUSE, and Amazon Linux 2). If immediate patching is not possible, restrict network access to services that process user-supplied images, implement file type validation before passing images to ImageMagick, or temporarily disable ImageMagick-based image processing if not critical (ImageMagick Advisory, Github Advisory, Red Hat Bugzilla).

The vulnerability received routine coverage from Linux distribution security teams, with patches issued by Debian (DSA-6158-1, DSA-6159-1, DLA-4497-1), Ubuntu (USN-8127-1, USN-8263-1), SUSE/openSUSE, and Amazon Linux 2. Red Hat tracked the issue via Bugzilla with medium severity. No notable independent researcher commentary or significant social media discussion has been identified beyond standard vulnerability aggregator coverage.