CVE-2021-3596 in ImageMagick
Summary
by MITRE • 02/24/2022
A NULL pointer dereference flaw was found in ImageMagick in versions prior to 7.0.10-31 in ReadSVGImage() in coders/svg.c. This issue is due to not checking the return value from libxml2's xmlCreatePushParserCtxt() and uses the value directly, which leads to a crash and segmentation fault.
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Analysis
by VulDB Data Team • 02/26/2022
The vulnerability identified as CVE-2021-3596 represents a critical NULL pointer dereference flaw within ImageMagick's SVG image processing functionality. This issue specifically affects versions prior to 7.0.10-31 and manifests within the ReadSVGImage() function located in the coders/svg.c file. The flaw stems from inadequate input validation and error handling practices that fail to properly check the return value from libxml2's xmlCreatePushParserCtxt() function. When this function fails to allocate memory or encounters parsing errors, it returns a NULL pointer which is then directly dereferenced by ImageMagick's processing logic, resulting in immediate system crash and segmentation fault conditions.
The technical nature of this vulnerability places it squarely within CWE-476, which defines NULL Pointer Dereference as a condition where a null pointer is dereferenced, leading to program termination. This flaw demonstrates a classic error handling weakness in software security architecture where developers assume that external library calls will always succeed without proper validation. The vulnerability operates at the intersection of XML parsing and image processing, creating a dangerous scenario where maliciously crafted SVG files can trigger the NULL pointer dereference through the libxml2 library interface. The exploitation requires only that an attacker be able to submit an SVG file to a vulnerable ImageMagick instance, making it particularly dangerous in web applications or file processing systems.
The operational impact of CVE-2021-3596 extends beyond simple system crashes to encompass potential denial of service conditions that can disrupt legitimate operations. When exploited, this vulnerability allows attackers to cause segmentation faults that terminate the ImageMagick process, effectively preventing further image processing operations. In environments where ImageMagick is used as a backend service for image manipulation, this can lead to complete service unavailability and significant operational disruption. The vulnerability also aligns with ATT&CK technique T1499.004, which covers Network Denial of Service, as the crash can be triggered through network-based file uploads or processing requests.
Mitigation strategies for this vulnerability primarily focus on immediate version updates to ImageMagick 7.0.10-31 or later, which contain the necessary patches to properly validate the return values from libxml2 functions. System administrators should also implement proper input validation and sanitization measures for SVG files, particularly in web applications where user uploads are processed. Additional protective measures include restricting file type processing capabilities, implementing sandboxing techniques for image processing operations, and deploying network monitoring to detect potential exploitation attempts. The fix addresses the core issue by ensuring that the return value from xmlCreatePushParserCtxt() is properly validated before any further processing occurs, thereby preventing the NULL pointer dereference that leads to system crashes and segmentation faults. Organizations should also consider implementing automated patch management systems to ensure rapid deployment of security updates across all affected systems and applications.