CVE-2021-20176 in ImageMagick
Summary
by MITRE • 02/06/2021
A flaw was found in ImageMagick in MagickCore/gem.c. An attacker who submits a crafted file that is processed by ImageMagick could trigger undefined behavior in the form of math division by zero. This would most likely lead to an impact to application availability, but could potentially cause other problems related to undefined behavior. This flaw affects ImageMagick versions prior to 7.0.10-56.
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Analysis
by VulDB Data Team • 02/25/2021
The vulnerability identified as CVE-2021-20176 represents a critical security flaw within ImageMagick's MagickCore component, specifically in the gem.c file that handles image processing operations. This issue stems from inadequate input validation when processing specially crafted image files, creating a scenario where mathematical operations can execute with invalid parameters. The flaw manifests as a division by zero condition during the processing of malformed image data, which fundamentally disrupts the application's execution flow and creates a potential vector for denial of service attacks. The vulnerability exists in versions of ImageMagick prior to 7.0.10-56, indicating that the developers were aware of this weakness and implemented fixes in subsequent releases.
The technical implementation of this vulnerability occurs within the MagickCore library's image processing pipeline where the gem.c module handles color space conversions and pixel manipulation operations. When an attacker submits a maliciously constructed image file, the processing routine fails to properly validate mathematical parameters, leading to a division by zero error that crashes the application or causes it to enter an undefined state. This undefined behavior can result in application termination, memory corruption, or other unpredictable system responses that directly impact service availability. The flaw demonstrates poor error handling practices and insufficient input sanitization, allowing malformed data to propagate through the processing chain without proper validation checks.
From an operational perspective, this vulnerability poses significant risks to systems that utilize ImageMagick for image processing, particularly in web applications, content management systems, and file upload services. The impact extends beyond simple availability disruption as the undefined behavior could potentially be exploited to execute arbitrary code or cause system instability. Attackers could leverage this flaw to perform denial of service attacks against web applications that process user-uploaded images, effectively rendering services unavailable to legitimate users. The vulnerability's exploitation requires minimal technical expertise, making it particularly dangerous in environments where image processing is a common operation and user input is not properly validated.
Security professionals should implement immediate mitigations including updating ImageMagick installations to version 7.0.10-56 or later, which contains the necessary patches to address the division by zero condition. Additionally, implementing input validation measures at the application level can provide defense in depth, ensuring that image files are properly sanitized before being passed to ImageMagick processing functions. Network-based protections such as web application firewalls can also help detect and block malicious image file uploads that may trigger this vulnerability. The flaw aligns with CWE-369, which describes the weakness of division by zero, and could potentially map to ATT&CK techniques related to denial of service and privilege escalation through application vulnerabilities. Organizations should also consider implementing sandboxed processing environments for image operations to limit the potential impact of any exploitation attempts.