CVE-2021-40211 in ImageMagick
Summary
by MITRE • 08/22/2023
An issue was discovered with ImageMagick 7.1.0-4 via Division by zero in function ReadEnhMetaFile of coders/emf.c.
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability CVE-2021-40211 represents a critical division by zero flaw within ImageMagick's Enhanced Metafile (EMF) coder module, specifically in the ReadEnhMetaFile function located at coders/emf.c. This issue arises when processing specially crafted EMF files that contain malformed data structures, causing the software to attempt division operations with zero as the divisor. The flaw exists in ImageMagick version 7.1.0-4 and potentially affects earlier versions within the same release series, making it a significant concern for systems that process untrusted image files through this library.
The technical implementation of this vulnerability stems from inadequate input validation within the EMF file parsing logic. When the ReadEnhMetaFile function encounters certain metafile records that specify invalid or zero-valued parameters, it proceeds to execute division operations without proper bounds checking or error handling. This fundamental programming oversight allows an attacker to craft malicious EMF files that deliberately include zero values in arithmetic operations, leading to a system crash or potential code execution depending on the underlying system behavior. The vulnerability demonstrates characteristics consistent with CWE-369, which specifically addresses the division by zero weakness where a division operation is performed with a zero divisor, potentially causing program termination or unpredictable behavior.
The operational impact of CVE-2021-40211 extends beyond simple denial of service scenarios, as it can be leveraged for more sophisticated attacks within systems that utilize ImageMagick for image processing. Web applications, content management systems, and file processing services that accept user-uploaded images may become vulnerable to remote code execution or system compromise if they process EMF files through the affected ImageMagick library. Attackers could exploit this vulnerability by uploading malicious EMF files to systems that automatically process these images, potentially leading to unauthorized access, data breaches, or complete system compromise. The vulnerability aligns with ATT&CK technique T1203, which involves using software exploitation to gain system access through code execution flaws in image processing libraries.
Mitigation strategies for CVE-2021-40211 should prioritize immediate patching of ImageMagick installations to versions that have addressed this division by zero condition. Organizations should implement strict input validation and file type filtering mechanisms to prevent processing of potentially malicious EMF files, particularly in web-facing applications. Network segmentation and access controls should be enforced to limit exposure of systems that process untrusted image content. Additionally, implementing sandboxing techniques for image processing operations can help contain potential exploitation attempts and prevent lateral movement within compromised systems. Security monitoring should include detection of unusual processing patterns or system crashes that may indicate exploitation attempts against this vulnerability, with particular attention to systems running ImageMagick versions prior to 7.1.0-5 where the fix has been implemented.