CVE-2013-6954 in Java SE
Summary
by MITRE
The png_do_expand_palette function in libpng before 1.6.8 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via (1) a PLTE chunk of zero bytes or (2) a NULL palette, related to pngrtran.c and pngset.c.
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Analysis
by VulDB Data Team • 06/10/2025
The vulnerability identified as CVE-2013-6954 affects the libpng library version 1.6.7 and earlier, representing a critical denial of service flaw that can be exploited remotely by attackers. This vulnerability resides within the png_do_expand_palette function, which is responsible for handling palette expansion operations during PNG image processing. The flaw manifests when the library encounters malformed PNG files containing specific invalid palette conditions that trigger unexpected behavior in the image decoding pipeline.
The technical implementation of this vulnerability stems from inadequate input validation within the pngrtran.c and pngset.c source files where the png_do_expand_palette function fails to properly handle edge cases involving palette data. Attackers can exploit this by crafting specially formatted PNG files containing either a PLTE chunk with zero bytes or a NULL palette reference, both of which cause the function to attempt dereferencing null pointers during the palette expansion process. This null pointer dereference results in immediate application crashes and system instability, effectively enabling a denial of service attack against systems processing PNG images.
From an operational impact perspective, this vulnerability poses significant risks to web servers, image processing applications, and any software systems that handle user-uploaded PNG files without proper input sanitization. The vulnerability is particularly dangerous in web environments where users can upload arbitrary image files, as attackers can systematically crash application services by uploading maliciously crafted PNG images. The flaw affects the core image processing functionality of applications using libpng, potentially leading to complete service disruption and requiring system administrators to restart affected services.
Security practitioners should note that this vulnerability aligns with CWE-476, which describes NULL pointer dereference conditions, and represents a classic example of insufficient input validation in image processing libraries. The attack surface extends beyond simple web applications to include any system that utilizes libpng for image handling, including mobile applications, desktop software, and server-side image processing services. Mitigation strategies should focus on upgrading to libpng version 1.6.8 or later, implementing proper input validation for all image files, and deploying intrusion detection systems to monitor for suspicious PNG file patterns.
The remediation approach requires immediate patching of affected systems and implementation of comprehensive image validation routines that check palette chunk integrity before processing. Organizations should also consider deploying web application firewalls and implementing strict file type validation to prevent exploitation attempts. Additionally, security teams should monitor for similar vulnerabilities in other image processing libraries and maintain updated threat intelligence regarding image-based attack vectors. This vulnerability demonstrates the importance of robust input validation in multimedia processing libraries and highlights the potential for seemingly benign image formats to become attack vectors when not properly sanitized.