CVE-2020-27764 in ImageMagick
Summary
by MITRE • 12/03/2020
In /MagickCore/statistic.c, there are several areas in ApplyEvaluateOperator() where a size_t cast should have been a ssize_t cast, which causes out-of-range values under some circumstances when a crafted input file is processed by ImageMagick. Red Hat Product Security marked this as Low severity because although it could potentially lead to an impact to application availability, no specific impact was shown in this case. This flaw affects ImageMagick versions prior to 6.9.10-69.
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Analysis
by VulDB Data Team • 12/12/2020
The vulnerability identified as CVE-2020-27764 represents a critical type casting issue within ImageMagick's MagickCore library, specifically in the statistic.c file where the ApplyEvaluateOperator() function processes image data. This flaw stems from improper type handling that can lead to integer overflow conditions when processing malformed input files, creating potential security implications for applications that rely on ImageMagick for image processing operations. The vulnerability manifests when crafted input files trigger scenarios where size_t variables are used in contexts where ssize_t would be more appropriate, particularly affecting the handling of image dimensions and memory allocations. The issue affects versions of ImageMagick prior to 6.9.10-69, indicating that this was a known problem that required specific patching to address the underlying type casting errors.
The technical implementation of this vulnerability involves the conversion of size_t to ssize_t in mathematical operations within the ApplyEvaluateOperator() function, where unsigned size_t values are used in contexts that require signed ssize_t values to properly handle negative results or boundary conditions. When processing maliciously crafted image files, these improper type casts can result in out-of-range values that may cause memory access violations or other undefined behaviors. The flaw operates by leveraging the difference between unsigned and signed integer representations, where size_t values can overflow and wrap around to extremely large positive numbers, while ssize_t correctly handles negative values that might occur during image processing calculations. This type casting error creates a pathway for potential denial of service conditions where the application may crash or become unresponsive during image processing operations.
From an operational perspective, this vulnerability presents a significant risk to systems that process untrusted image files, particularly in web applications, content management systems, and any environment where users can upload or submit image data. The low severity classification by Red Hat Product Security reflects the fact that no specific exploit was demonstrated that could lead to arbitrary code execution or privilege escalation, however the potential for availability impact remains substantial. Attackers could potentially craft malicious image files that, when processed by vulnerable ImageMagick installations, would cause application crashes or resource exhaustion, leading to denial of service conditions that could affect legitimate users and system availability. The vulnerability is particularly concerning in server environments where automated image processing occurs, as it could be exploited to disrupt services at scale.
Mitigation strategies for CVE-2020-27764 primarily focus on updating ImageMagick installations to version 6.9.10-69 or later, which contains the necessary patches to correct the type casting errors in the statistic.c file. Organizations should also implement input validation measures to filter or reject suspicious image files before processing, particularly in environments where untrusted inputs are common. Additional protective measures include running ImageMagick processes with restricted privileges, implementing memory limits and timeouts for image processing operations, and monitoring for unusual resource consumption patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-191, Integer Underflow or Wraparound, and may map to ATT&CK techniques involving privilege escalation or denial of service through application vulnerabilities. Security teams should also consider implementing network segmentation and access controls to limit exposure of systems running vulnerable ImageMagick versions, while maintaining regular patch management procedures to address similar issues that may arise in the future.