CVE-2016-6911 in GD Graphics Library
Summary
by MITRE
The dynamicGetbuf function in the GD Graphics Library (aka libgd) before 2.2.4 allows remote attackers to cause a denial of service (out-of-bounds read) via a crafted TIFF image.
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Analysis
by VulDB Data Team • 05/14/2026
The CVE-2016-6911 vulnerability represents a critical out-of-bounds read flaw within the GD Graphics Library, specifically affecting the dynamicGetbuf function in versions prior to 2.2.4. This vulnerability exists within the library's handling of TIFF image files, making it particularly dangerous as TIFF format is widely used across various applications and systems for image processing. The flaw allows remote attackers to craft malicious TIFF images that trigger memory access violations when the library attempts to process these files, potentially leading to system instability or complete service disruption. This vulnerability falls under the CWE-125 Out-of-bounds Read category, which is classified as a memory safety issue that can lead to unpredictable behavior and system compromise.
The technical implementation of this vulnerability stems from inadequate input validation within the dynamicGetbuf function, which fails to properly bounds-check memory allocations when processing TIFF image data structures. When a crafted TIFF file is loaded, the function attempts to read memory locations beyond the allocated buffer boundaries, causing the application to access invalid memory regions. This type of vulnerability is particularly concerning in web applications and image processing services that rely on libgd for handling user-uploaded images, as attackers can exploit this flaw without requiring any special privileges or authentication. The out-of-bounds read can result in application crashes, data corruption, or potentially enable more sophisticated attacks depending on the execution environment and memory layout.
The operational impact of CVE-2016-6911 extends beyond simple denial of service, as it can be leveraged in broader attack chains within the ATT&CK framework under the T1499.004 technique for network denial of service. Systems utilizing libgd for image processing, including web servers, content management systems, and image processing applications, become vulnerable to remote exploitation when they accept and process TIFF files from untrusted sources. This vulnerability affects a wide range of software ecosystems since libgd is a fundamental component in many open-source and commercial applications, making the potential attack surface extensive. Organizations running web services that process image uploads, especially those that support TIFF format, are at significant risk as attackers can cause sustained service disruption through carefully crafted malicious files.
Mitigation strategies for CVE-2016-6911 primarily focus on immediate remediation through version updates to libgd 2.2.4 or later, which contain the necessary patches to address the bounds-checking issues in the dynamicGetbuf function. System administrators should prioritize patching affected applications and services that utilize libgd, particularly those handling user-uploaded content or processing external image files. Additional defensive measures include implementing strict input validation and sanitization for image file types, disabling TIFF format support where possible, and deploying network-based intrusion detection systems to monitor for suspicious TIFF file patterns. Security monitoring should focus on detecting attempts to upload or process malformed TIFF files, as these activities may indicate exploitation attempts. Organizations should also consider implementing application-level sandboxing or containerization for image processing functions to limit the potential impact of any successful exploitation attempts.