CVE-2017-6362 in libgd2
Summary
by MITRE
Double free vulnerability in the gdImagePngPtr function in libgd2 before 2.2.5 allows remote attackers to cause a denial of service via vectors related to a palette with no colors.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/28/2022
The CVE-2017-6362 vulnerability represents a critical double free error in the libgd2 graphics library that affects applications handling png image data. This flaw specifically resides within the gdImagePngPtr function, which is responsible for encoding png images from memory. The vulnerability manifests when processing png images that contain a palette with no colors, creating a scenario where memory allocated for image processing is freed twice during the execution flow. This type of memory corruption vulnerability falls under the CWE-415 category of double free conditions, where the same memory block is deallocated multiple times, potentially leading to unpredictable behavior in the application.
The technical exploitation of this vulnerability occurs during the png image processing pipeline when the library encounters malformed palette data. When a png image is processed with an empty color palette, the gdImagePngPtr function fails to properly validate the palette structure before proceeding with memory allocation and deallocation operations. The double free condition arises because the function allocates memory for palette handling and then attempts to free the same memory block twice during the image encoding process. This flaw is particularly dangerous because it can be triggered remotely through image upload mechanisms or image processing services that utilize libgd2.
The operational impact of CVE-2017-6362 extends beyond simple denial of service to potentially enable more sophisticated attacks depending on the application context. Remote attackers can leverage this vulnerability to crash applications that rely on libgd2 for image processing, resulting in service disruption and potential availability issues for web applications, content management systems, or any software that handles png image uploads. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, where adversaries exploit memory corruption flaws to disrupt system availability. Applications using vulnerable versions of libgd2 may experience complete service termination or memory corruption that could lead to privilege escalation in certain environments.
Mitigation strategies for this vulnerability require immediate patching of affected libgd2 installations to version 2.2.5 or later, which contains the necessary memory management fixes. System administrators should prioritize updating all applications that depend on libgd2, particularly web servers, image processing services, and content management platforms. Additionally, implementing input validation controls that sanitize png image uploads can provide defense-in-depth measures, though the primary solution remains the library update. Organizations should also consider implementing monitoring for unusual application crashes or memory allocation patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper memory management in graphics libraries and highlights the need for comprehensive testing of edge cases in image processing functions. Security teams should conduct vulnerability assessments to identify all systems using affected versions of libgd2 and establish monitoring procedures to detect potential exploitation attempts.