CVE-2016-6906 in GD Graphics Library
Summary
by MITRE
The read_image_tga function in gd_tga.c 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 TGA file, related to the decompression buffer.
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Analysis
by VulDB Data Team • 09/08/2020
The vulnerability identified as CVE-2016-6906 represents a critical out-of-bounds read flaw within the GD Graphics Library, specifically affecting the read_image_tga function in gd_tga.c. This issue exists in versions prior to 2.2.4 and exposes systems to remote denial of service attacks through manipulation of TGA image files. The flaw occurs during the decompression buffer processing phase, where the library fails to properly validate input parameters before attempting to read from memory locations beyond the allocated buffer boundaries. The vulnerability stems from inadequate bounds checking mechanisms that allow attackers to craft malicious TGA files with malformed header data or incorrect size specifications, leading to unauthorized memory access patterns.
The technical exploitation of this vulnerability follows a well-defined attack pattern that aligns with CWE-129, which addresses improper validation of array indices or buffer boundaries. Attackers can construct specially crafted TGA files containing oversized or malformed dimension fields that, when processed by the vulnerable library, trigger the out-of-bounds memory read. This behavior maps directly to ATT&CK technique T1203, which involves the exploitation of memory corruption vulnerabilities for denial of service purposes. The flaw demonstrates a classic buffer over-read condition where the decompression routine attempts to access memory locations that were never properly allocated or validated, creating opportunities for system instability and potential information disclosure.
From an operational impact perspective, this vulnerability poses significant risks to web applications, content management systems, and any software platforms that rely on libgd for image processing. When exploited, the out-of-bounds read can cause application crashes, leading to complete service unavailability for legitimate users. The remote nature of the attack means that malicious actors can trigger the vulnerability without requiring physical access to the target system, making it particularly dangerous in web-facing environments. Systems processing user-uploaded TGA images become prime targets, as the vulnerability can be exploited through simple file uploads without requiring authentication or specialized privileges.
Mitigation strategies for CVE-2016-6906 primarily focus on immediate version updates to libgd 2.2.4 or later, which contain the necessary patches to address the buffer validation issues. Organizations should implement comprehensive patch management procedures to ensure all affected systems receive updates promptly. Additional protective measures include input validation at multiple layers, where TGA file headers are strictly validated before processing, and the implementation of memory protection mechanisms such as address space layout randomization and stack canaries. Network-level defenses can be enhanced through content filtering systems that scan for known malicious TGA file patterns and implement rate limiting for image upload operations. The vulnerability also underscores the importance of regular security assessments and dependency monitoring to identify and remediate similar issues in third-party libraries before they can be exploited by threat actors.