CVE-2016-2191 in OptiPNG
Summary
by MITRE
The bmp_read_rows function in pngxtern/pngxrbmp.c in OptiPNG before 0.7.6 allows remote attackers to cause a denial of service (invalid memory write and crash) via a series of delta escapes in a crafted BMP image.
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Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-2191 represents a critical memory corruption flaw within the OptiPNG image processing library that affects versions prior to 0.7.6. This vulnerability specifically targets the bmp_read_rows function located in the pngxtern/pngxrbmp.c source file, which is responsible for handling bitmap image format processing within the optimization pipeline. The flaw manifests when the software encounters a specially crafted BMP image containing a sequence of delta escapes that exceed the bounds of allocated memory buffers, creating a condition where invalid memory writes occur during the image decompression process. The vulnerability stems from inadequate input validation and boundary checking mechanisms within the bitmap row reading functionality, which fails to properly sanitize the delta escape sequences present in the malicious image payload.
The technical exploitation of this vulnerability occurs through a carefully constructed BMP image file that contains malformed delta escape sequences designed to trigger memory corruption during the decompression phase. When OptiPNG processes such an image, the bmp_read_rows function attempts to write data beyond the allocated memory boundaries, resulting in invalid memory writes that ultimately lead to application crashes and system instability. This type of vulnerability falls under the category of buffer overflow conditions as classified by CWE-121, specifically representing a heap-based buffer overflow scenario where the software writes beyond the bounds of allocated memory regions. The vulnerability is particularly dangerous because it can be triggered remotely through network-based image processing workflows, making it an attractive target for attackers seeking to disrupt services or cause denial of service conditions.
The operational impact of CVE-2016-2191 extends beyond simple application crashes to potentially enable more sophisticated attack vectors within systems that rely on OptiPNG for image processing. Organizations utilizing this library in automated workflows, web applications, or content management systems face significant risk of service disruption when processing untrusted image inputs. The vulnerability can be leveraged by attackers to create persistent denial of service conditions that may require system restarts or manual intervention to resolve. From an attacker's perspective, this represents a low-effort, high-impact method of service disruption that aligns with ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability's remote exploitability makes it particularly concerning for web applications that process user-uploaded images, as it can be used to systematically disrupt image processing services and potentially impact business operations.
Mitigation strategies for CVE-2016-2191 primarily focus on upgrading to OptiPNG version 0.7.6 or later, which includes proper input validation and boundary checking mechanisms that prevent the invalid memory write conditions. System administrators should implement comprehensive patch management processes to ensure all affected systems receive the necessary updates promptly. Additionally, input sanitization measures such as image format validation, size limits, and content scanning should be implemented as defensive controls to prevent malicious images from reaching the vulnerable processing functions. Network-level protections including web application firewalls and image processing gateways can provide additional layers of defense by filtering suspicious image content before it reaches the OptiPNG processing pipeline. The vulnerability highlights the importance of robust memory safety practices in image processing libraries and demonstrates how seemingly benign input validation gaps can result in critical system instability. Organizations should also consider implementing automated monitoring and alerting systems to detect potential exploitation attempts and ensure rapid response to any service disruption incidents.