CVE-2007-2756 in GD Graphics Library
Summary
by MITRE
The gdPngReadData function in libgd 2.0.34 allows user-assisted attackers to cause a denial of service (CPU consumption) via a crafted PNG image with truncated data, which causes an infinite loop in the png_read_info function in libpng.
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Analysis
by VulDB Data Team • 08/10/2022
The vulnerability identified as CVE-2007-2756 represents a critical denial of service flaw affecting the libgd graphics library version 2.0.34 and earlier. This issue specifically targets the gdPngReadData function which processes PNG image files through integration with the libpng library. The vulnerability arises from insufficient input validation and error handling mechanisms within the image parsing pipeline, creating a condition where malformed PNG data can trigger unexpected behavior in the underlying graphics processing stack.
The technical flaw manifests when a crafted PNG image containing truncated data is processed by the vulnerable libgd library. During the parsing operation, the gdPngReadData function fails to properly validate the integrity of the PNG data stream, allowing the libpng library to enter an infinite loop within the png_read_info function. This occurs because the malformed data structure causes the PNG parser to continuously attempt to read information from what appears to be a valid PNG header but contains corrupted or incomplete data segments that cannot be properly interpreted. The infinite loop consumes excessive CPU resources and effectively renders the application or system processing the image unresponsive, creating a classic denial of service condition.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can affect any application or service that relies on libgd for PNG image processing. Systems using web servers, image processing applications, or any software that accepts user-uploaded PNG files become vulnerable to this attack vector. The attacker need only provide a specially crafted PNG file to trigger the condition, making this a user-assisted denial of service vulnerability that can be exploited through various attack surfaces including web uploads, file processing services, or content management systems. This vulnerability particularly affects environments where automated image processing occurs, as the infinite loop can cause cascading failures across multiple processing threads or processes.
Mitigation strategies for CVE-2007-2756 primarily focus on upgrading to patched versions of libgd and libpng libraries, with the vulnerability being resolved in libgd version 2.0.35 and later. Organizations should implement input validation measures to verify PNG file integrity before processing, including checking file headers and implementing timeouts for image processing operations. Network-level defenses can include content filtering systems that scan for suspicious PNG file characteristics and implement rate limiting for image upload operations. From a cybersecurity perspective, this vulnerability aligns with CWE-835, which addresses infinite loops or iterations without proper termination conditions. The attack pattern follows typical denial of service methodologies described in the MITRE ATT&CK framework under the service stoppage category, where adversaries leverage software weaknesses to exhaust system resources and disrupt normal operations. Regular security assessments and patch management programs become essential defensive measures to prevent exploitation of this and similar vulnerabilities in legacy software systems.