CVE-2019-6978 in GD Graphics Library
Summary
by MITRE
The GD Graphics Library (aka LibGD) 2.2.5 has a double free in the gdImage*Ptr() functions in gd_gif_out.c, gd_jpeg.c, and gd_wbmp.c. NOTE: PHP is unaffected.
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Analysis
by VulDB Data Team • 07/03/2023
The vulnerability identified as CVE-2019-6978 represents a critical double free condition within the GD Graphics Library version 2.2.5, specifically affecting the gdImage*Ptr() functions across multiple output modules. This flaw manifests in three distinct files: gd_gif_out.c, gd_jpeg.c, and gd_wbmp.c, where improper memory management leads to the same memory block being freed twice during image processing operations. The double free vulnerability occurs when the library's image output functions handle memory allocation and deallocation without proper validation of previously freed memory pointers, creating a scenario where the same memory address is passed to the free() function twice. This condition fundamentally undermines the memory management integrity of the library and creates opportunities for arbitrary code execution or system instability.
The technical nature of this vulnerability aligns with CWE-415, which specifically addresses double free conditions in memory management, and represents a classic example of improper memory handling that can be exploited through carefully crafted image data inputs. The flaw operates at the core of the library's image processing pipeline where it handles various graphic formats including gif, jpeg, and wbmp outputs. When an application processes malformed image data through these specific functions, the library's internal memory management routines fail to track previously freed memory blocks properly, resulting in the second free() call attempting to deallocate memory that has already been released to the system's heap manager. This memory corruption scenario creates undefined behavior that adversaries can potentially leverage to execute malicious code or cause denial of service conditions.
The operational impact of CVE-2019-6978 extends beyond simple library functionality degradation, as it affects any application or system that relies on the GD Graphics Library for image processing tasks. While PHP is unaffected by this specific vulnerability according to the description, numerous other programming languages and systems that directly utilize the LibGD library remain at risk, including applications written in C, C++, and other languages that interface with the library's C API. The vulnerability's exploitation potential is particularly concerning because it can be triggered through image file inputs that are processed by applications using LibGD, making it a significant threat vector for web applications, image processing services, and any system that handles user-uploaded or externally sourced image files. Attackers can craft malicious image files that, when processed by vulnerable systems, trigger the double free condition and potentially achieve remote code execution or system compromise.
Mitigation strategies for this vulnerability require immediate attention from system administrators and software maintainers. The most effective approach involves upgrading to a patched version of the GD Graphics Library where the double free conditions have been addressed through proper memory management implementation and pointer validation. Organizations should also implement input validation measures to filter potentially malicious image files before they reach the LibGD processing functions, though this approach provides only partial protection as the vulnerability lies within the library's core functionality. Additionally, runtime protections such as address space layout randomization and stack canaries can help mitigate exploitation attempts, while monitoring systems should be deployed to detect unusual memory allocation patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper memory management practices in system libraries and highlights the need for comprehensive security testing of core components that handle user inputs, particularly in graphics processing libraries that are widely used across different platforms and applications.