CVE-2016-6912 in GD Graphics Library
Summary
by MITRE
Double free vulnerability in the gdImageWebPtr function in the GD Graphics Library (aka libgd) before 2.2.4 allows remote attackers to have unspecified impact via large width and height values.
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Analysis
by VulDB Data Team • 05/14/2026
The CVE-2016-6912 vulnerability represents a critical double free condition within the GD Graphics Library, specifically affecting the gdImageWebPtr function in versions prior to 2.2.4. This flaw exists in the library's handling of image dimensions, where the software fails to properly validate or manage memory allocation when processing images with excessively large width and height parameters. The vulnerability stems from improper memory management practices that allow attackers to manipulate the library's internal state through crafted image data, potentially leading to arbitrary code execution or system compromise. The GD Graphics Library serves as a fundamental component for image processing across numerous web applications and systems, making this vulnerability particularly concerning for widespread exploitation.
The technical implementation of this vulnerability involves the gdImageWebPtr function's inadequate handling of integer overflow conditions when processing image dimensions. When attackers provide large width and height values, the library's memory allocation routines become susceptible to double free errors where the same memory block gets freed twice during the image processing workflow. This occurs because the library does not properly validate the input parameters against system memory limits, allowing malicious input to trigger memory corruption conditions that can be exploited by remote attackers. The vulnerability manifests during the image creation process when the library attempts to allocate memory for image data structures, where the double free condition creates a state where freed memory can be reallocated and manipulated by an attacker.
The operational impact of CVE-2016-6912 extends beyond simple memory corruption, as it can potentially enable remote code execution in vulnerable systems. Attackers can leverage this vulnerability by submitting specially crafted images to web applications that utilize the affected GD Graphics Library version, triggering the double free condition during image processing. The unspecified impact mentioned in the vulnerability description reflects the broad range of potential consequences including denial of service, privilege escalation, or complete system compromise depending on the target environment and execution context. This vulnerability particularly affects web applications that accept user-uploaded images or process external image data, making it a significant threat to web server security and application integrity.
Mitigation strategies for CVE-2016-6912 require immediate patching of affected systems to upgrade to GD Graphics Library version 2.2.4 or later, which contains the necessary memory management fixes. Organizations should implement input validation controls to limit image dimensions and prevent malicious values from reaching the vulnerable library functions. Network-based mitigations can include implementing image validation proxies or content filtering systems that analyze uploaded images for suspicious parameters before processing. The vulnerability aligns with CWE-415 which addresses double free conditions in memory management, and represents a classic example of improper resource management that can be exploited through the ATT&CK technique of command and control through application layer protocols. Security teams should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the exploitability of memory corruption vulnerabilities in affected environments.