CVE-2025-55212: ImageMagick affected by divide-by-zero in ThumbnailImage via montage -geometry ":" leads to crash

Summary Passing a geometry string containing only a colon (":") to montage -geometry leads GetGeometry() to set width/height to 0. Later, ThumbnailImage() divides by these zero dimensions, triggering a crash (SIGFPE/abort), resulting in a denial of service.

Details Root Cause 1. montage -geometry ":" ... reaches MagickCore/geometry.c:GetGeometry(). 2. StringToDouble/InterpretLocaleValue parses ":" as 0.0; then: https://github.com/ImageMagick/ImageMagick/blob/0ba1b587be17543b664f7ad538e9e51e0da59d17/MagickCore/geometry.c#L355 WidthValue (and/or HeightValue) is set with a zero dimension. 3. In MagickCore/resize.c:ThumbnailImage(), the code computes: https://github.com/ImageMagick/ImageMagick/blob/0ba1b587be17543b664f7ad538e9e51e0da59d17/MagickCore/resize.c#L4625-L4629 causing a division by zero and immediate crash.

The issue is trivially triggerable without external input files (e.g., using xc:white).

Reproduction Environment Version: ImageMagick 7.1.2-1 (Beta) Q16-HDRI x8664 0ba1b587b:20250812 https://imagemagick.org Features: Cipher DPC HDRI Delegates (built-in): bzlib fontconfig freetype jbig jng jpeg lcms lzma pangocairo png tiff x xml zlib Compiler: clang (14.0.0) OS/Arch: Linux x8664 Steps ./bin/magick montage -geometry : xc:white null: Observed result IOT instruction (core dumped) (Environment-dependent: SIGFPE/abort may be observed.)

PoC No external file required; the pseudo image xc:white suffices: ./bin/magick montage -geometry : xc:white null:

Impact - Denial of Service: A divide-by-zero in ThumbnailImage() causes immediate abnormal termination (e.g., SIGFPE/abort), crashing the ImageMagick process.

Suggested fix Defensively reject zero dimensions early in ThumbnailImage(): c if ((columns == 0) || (rows == 0)) { (void) ThrowMagickException(exception, GetMagickModule(), OptionError, "InvalidGeometry", "thumbnail requires non-zero dimensions: %.20gx%.20g", (double) columns, (double) rows); return (Image ) NULL; } Additionally, consider tightening validation in GetGeometry() so that colon-only (and similar malformed) inputs do not yield WidthValue/HeightValue with zero, or are rejected outright. Variants like "x:" or ":x" may also need explicit handling (maintainer confirmation requested).

Credits Team Daemon Fuzz Hunters Bug Hunting Master Program, HSpace/Findthegap <br>

Woojin Park @jin-156 1203kids@gmail.com

Hojun Lee @leehohojune leehojune@korea.ac.kr

Youngin Won @amethyst0225 youngin04@korea.ac.kr

Siyeon Han @hanbunny kokosyeon@gmail.com