CVE-2016-3981 in OptiPNG
Summary
by MITRE
Heap-based buffer overflow in the bmp_read_rows function in pngxrbmp.c in OptiPNG before 0.7.6 allows remote attackers to cause a denial of service (out-of-bounds read or write access and crash) or possibly execute arbitrary code via a crafted image file.
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Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-3981 represents a critical heap-based buffer overflow within the OptiPNG image processing library, specifically affecting the bmp_read_rows function in the pngxrbmp.c source file. This flaw exists in versions prior to 0.7.6 and demonstrates a classic memory corruption vulnerability that can be exploited through maliciously crafted image files. The vulnerability stems from inadequate bounds checking during the processing of bitmap image data, where the application fails to properly validate the size and structure of input image files before attempting to read or write memory segments.
The technical implementation of this vulnerability occurs when OptiPNG processes bitmap images that contain malformed data structures, particularly in the row data handling mechanism. When the bmp_read_rows function attempts to process image rows without sufficient validation of the expected data size, it can overwrite adjacent heap memory locations or read beyond allocated buffer boundaries. This memory corruption can manifest in multiple ways including out-of-bounds read operations that may expose sensitive memory contents, out-of-bounds write operations that can corrupt program state, or more severely, arbitrary code execution if the overflow allows an attacker to control instruction pointers or overwrite critical program structures. The heap-based nature of the vulnerability means that the attack surface is particularly broad as heap memory management can be unpredictable and difficult to secure completely.
From an operational perspective, this vulnerability presents significant risks to systems that process untrusted image files, particularly those that might be subject to automated image processing workflows or web-based image handling systems. Attackers can leverage this flaw by crafting specially formatted bitmap images that, when processed by vulnerable OptiPNG versions, trigger the buffer overflow condition. The potential impact extends beyond simple denial of service to include remote code execution capabilities, making this vulnerability particularly dangerous in environments where image processing occurs automatically or where users can upload images to systems that may process them with OptiPNG. The vulnerability affects not only direct applications using OptiPNG but also any system or service that relies on OptiPNG for image optimization or conversion tasks, including web applications, content management systems, and automated image processing pipelines.
The vulnerability aligns with CWE-121, Heap-based Buffer Overflow, which specifically addresses buffer overflows occurring in heap memory regions, and can be mapped to ATT&CK technique T1203, Exploitation for Client Execution, when considering how attackers might leverage this vulnerability through image file processing. Mitigation strategies should focus on immediate patching to OptiPNG versions 0.7.6 or later where the buffer overflow has been corrected through proper bounds checking and input validation. Additionally, system administrators should implement defensive measures such as input sanitization for image files, restricting image processing to trusted sources, and employing sandboxed environments for image handling operations. Network-level defenses including web application firewalls and content filtering systems can also help prevent exploitation by blocking suspicious image file uploads or processing requests that might trigger the vulnerable code path. Organizations should also consider implementing memory protection mechanisms like stack canaries, address space layout randomization, and heap protection features to reduce the effectiveness of potential exploitation attempts.