CVE-2017-16938 in OptiPNG
Summary
by MITRE
A global buffer overflow in OptiPNG 0.7.6 allows remote attackers to cause a denial-of-service attack or other unspecified impact with a maliciously crafted GIF format file, related to an uncontrolled loop in the LZWReadByte function of the gifread.c file.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/16/2023
The vulnerability identified as CVE-2017-16938 represents a critical buffer overflow flaw within OptiPNG version 0.7.6 that stems from improper handling of maliciously crafted GIF format files. This issue resides in the gifread.c source file where the LZWReadByte function contains an uncontrolled loop that fails to properly validate input data boundaries. The flaw manifests when the application processes compressed data streams using the LZW (Lempel-Ziv-Welch) compression algorithm commonly employed in GIF image format specifications. When a specially crafted GIF file is processed, the vulnerable code executes an infinite loop that consumes excessive system resources and ultimately leads to application termination.
The technical exploitation of this vulnerability occurs through the manipulation of GIF file headers and compressed data segments that trigger the problematic LZW decompression routine. The uncontrolled loop within LZWReadByte function fails to implement proper boundary checks or iteration limits, allowing attackers to craft input data that causes the decompression algorithm to enter an infinite processing state. This condition results in the application consuming all available CPU cycles and memory resources, effectively rendering the system unavailable to process legitimate requests. The vulnerability specifically maps to CWE-121, which describes heap-based buffer overflow conditions, and CWE-674, which addresses uncontrolled recursion or loops in software components. The flaw demonstrates characteristics of a denial-of-service attack vector where the attacker can cause system instability without requiring elevated privileges or complex exploitation techniques.
From an operational impact perspective, this vulnerability poses significant risks to systems that process or validate GIF images through OptiPNG software, particularly in web applications, content management systems, and automated image processing pipelines. The vulnerability can be exploited remotely through any application that utilizes OptiPNG for image optimization or validation, including web servers that accept user-uploaded GIF files, email filtering systems, and digital asset management platforms. The attack surface extends beyond simple file processing to encompass any service that might execute OptiPNG on untrusted input data, potentially leading to cascading failures in dependent systems. The vulnerability affects systems running OptiPNG 0.7.6 and earlier versions, with the issue being resolved through proper input validation and loop boundary enforcement in the decompression routines.
Mitigation strategies for CVE-2017-16938 should prioritize immediate software updates to OptiPNG version 0.7.7 or later, which contains the necessary patches to address the uncontrolled loop condition in the LZWReadByte function. System administrators should implement input validation measures that filter or reject suspicious GIF files before processing, particularly those with unusual compression ratios or malformed headers. Network-based defenses can include implementing rate limiting and resource monitoring to detect and prevent exploitation attempts. The vulnerability aligns with ATT&CK technique T1499.001, which covers network denial of service attacks, and T1059.007, covering script-based attacks that may leverage such vulnerabilities. Organizations should also consider deploying intrusion detection systems that can identify patterns consistent with this specific buffer overflow exploitation attempt, monitoring for unusual CPU utilization spikes and memory consumption patterns that indicate potential exploitation. Regular security assessments and penetration testing should verify that patched systems remain resilient against similar vulnerabilities in related software components.