CVE-2026-25969: 
C# vulnerability analysis and mitigation

CVE-2026-25969 is a memory leak vulnerability in ImageMagick's ASHLAR image coder that can lead to denial of service. The flaw exists in coders/ashlar.c, where the WriteASHLARImage function allocates a structure but fails to release the allocated memory when an exception is thrown. All ImageMagick versions prior to 7.1.2-15 are affected, as are Magick.NET NuGet packages prior to version 14.10.3. The vulnerability was disclosed on February 23–24, 2026, and carries a CVSS v3.1 base score of 5.3 (Moderate) per the GitHub Advisory, though NVD rates it 7.5 (High) (GitHub Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-401 (Missing Release of Memory after Effective Lifetime) and CWE-772 (Missing Release of Resource after Effective Lifetime). Within coders/ashlar.c, the WriteASHLARImage function allocates heap memory for a structure during ASHLAR image processing; however, the exception-handling code path does not include the corresponding deallocation, leaving the memory unreachable. Valgrind analysis confirmed the leak: 17,232 bytes across 4 blocks remained in use at exit after 4,781 allocations and only 4,777 frees. The vulnerability is exploitable over the network without authentication or user interaction, requiring only that a crafted ASHLAR image file be submitted for processing (GitHub Advisory, Github Advisory).

The vulnerability's impact is limited to availability — there is no confidentiality or integrity exposure. An attacker who can supply crafted ASHLAR image files to a vulnerable ImageMagick instance can trigger repeated memory leaks, gradually exhausting process memory and potentially causing ImageMagick processes to crash or become unresponsive, resulting in a denial of service. Systems that automatically process untrusted image uploads (e.g., web applications, media pipelines) are at greatest risk, as repeated submissions can compound memory exhaustion (GitHub Advisory, Red Hat Bugzilla).

1. Identify target: Locate a service or application that uses a vulnerable version of ImageMagick (< 7.1.2-15) or Magick.NET (< 14.10.3) to process user-supplied image files, such as an image upload endpoint.
2. Craft malicious ASHLAR file: Create or obtain an ASHLAR-format image file designed to trigger an exception during the WriteASHLARImage processing path, causing the memory allocation to be abandoned without release.
3. Submit the file repeatedly: Upload or submit the crafted ASHLAR file to the target application multiple times. Each processing attempt leaks a small amount of heap memory (approximately 17 KB per instance based on Valgrind output).
4. Exhaust memory: Through repeated submissions, accumulate leaked memory until the ImageMagick process or the hosting application runs out of available memory, causing crashes or unresponsiveness (denial of service) (GitHub Advisory).

• Process Behavior: ImageMagick processes exhibiting steadily increasing memory consumption over time without corresponding release; processes eventually crashing or becoming unresponsive when processing ASHLAR image files.
• Logs: Application or system logs showing repeated processing of ASHLAR-format image files from the same source IP; error or exception messages originating from coders/ashlar.c or WriteASHLARImage.
• System: Out-of-memory (OOM) killer events in Linux system logs (/var/log/syslog or dmesg) attributable to ImageMagick worker processes; unexpected process terminations of image-processing services.
• Network: High-frequency image upload requests, particularly with ASHLAR file extensions or MIME types, from a single or small set of source addresses.

The primary remediation is to upgrade ImageMagick to version 7.1.2-15 or later, which contains the patch that properly releases allocated memory in the exception-handling path of WriteASHLARImage. Users of the Magick.NET NuGet packages should upgrade to version 14.10.3 or later. As a workaround where immediate patching is not possible, organizations should restrict or disable processing of ASHLAR image files, implement rate limiting on image upload endpoints, and ensure ImageMagick processes run with memory limits (e.g., via ulimit or container resource constraints) to reduce the impact of memory exhaustion. Linux distribution packages (Debian, SUSE, openSUSE) have also released updated packages (GitHub Advisory, Github Advisory).

The vulnerability was reported by security researcher unbengable12 and published by ImageMagick maintainer dlemstra via GitHub Security Advisories on February 23, 2026. Red Hat tracked the issue via Bugzilla and classified it as medium severity. Distribution vendors including SUSE, openSUSE, and Debian issued security updates for their ImageMagick packages. No significant broader media coverage or notable social media discussion has been observed beyond standard vulnerability tracking and distribution advisory channels (GitHub Advisory, Red Hat Bugzilla).