CVE-2016-9933 in macOS
Summary
by MITRE
Stack consumption vulnerability in the gdImageFillToBorder function in gd.c in the GD Graphics Library (aka libgd) before 2.2.2, as used in PHP before 5.6.28 and 7.x before 7.0.13, allows remote attackers to cause a denial of service (segmentation violation) via a crafted imagefilltoborder call that triggers use of a negative color value.
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Analysis
by VulDB Data Team • 11/03/2022
The CVE-2016-9933 vulnerability represents a critical stack consumption flaw within the GD Graphics Library implementation, specifically affecting the gdImageFillToBorder function in gd.c. This vulnerability exists in libgd versions prior to 2.2.2 and impacts PHP installations before 5.6.28 and 7.x before 7.0.13, creating a significant attack surface for remote threat actors seeking to disrupt system availability. The flaw manifests when a crafted imagefilltoborder call is executed, triggering an improper handling of negative color values that leads to excessive stack memory consumption. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, where the improper validation of input parameters results in memory corruption. The attack vector leverages the graphics processing capabilities of web applications that utilize GD library functions, making it particularly dangerous in web environments where image manipulation is common.
The technical exploitation of this vulnerability occurs through the manipulation of color parameters in the gdImageFillToBorder function, where negative color values are not properly validated or sanitized before being processed. When such values are passed to the function, the internal stack memory allocation becomes corrupted, leading to a segmentation fault that crashes the application process. The vulnerability's impact extends beyond simple application crashes to potentially enable more sophisticated attacks when combined with other exploitation techniques. This flaw aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign graphics processing functions can be weaponized for system disruption. The stack consumption pattern indicates that the vulnerability does not directly enable code execution but instead exhausts available stack resources, causing the targeted process to terminate abruptly.
The operational impact of CVE-2016-9933 is significant for web applications that rely on image processing capabilities, particularly those handling user-uploaded content or dynamic image generation. Attackers can leverage this vulnerability to perform denial of service attacks against web servers, causing service interruptions that may affect availability for legitimate users. The vulnerability affects a wide range of PHP-based applications including content management systems, e-commerce platforms, and web applications that utilize GD library functions for image manipulation. Organizations running affected versions of PHP and libgd are particularly vulnerable, as the flaw exists in the core graphics processing libraries that many applications depend upon. The remediation process requires updating to patched versions of both PHP and libgd, with careful consideration of compatibility issues in existing applications that may depend on the vulnerable behavior. Security teams should prioritize patching this vulnerability as it represents a straightforward path to service disruption that can be exploited without requiring advanced technical skills or extensive reconnaissance.
The broader implications of this vulnerability highlight the importance of proper input validation in graphics processing libraries and the potential for seemingly innocuous functions to become attack vectors. This flaw demonstrates how memory handling issues in system libraries can cascade into application-level denial of service conditions, emphasizing the need for comprehensive security testing of third-party libraries. Organizations should implement robust monitoring for unusual memory consumption patterns and ensure that their web application security practices include regular updates of core libraries. The vulnerability also underscores the importance of following security best practices such as input sanitization and proper error handling in graphics processing functions. This particular flaw serves as a reminder that even specialized libraries used for image manipulation require rigorous security review and testing to prevent exploitation through stack-based memory corruption attacks that can be easily triggered by malformed input parameters.