CVE-2026-106118 in ImageSharp
Summary
by MITRE • 10/06/2026
ImageSharp is a 2D graphics library. From 3.0.0 until 4.1.1, tiled TIFF decoding allocates a destination buffer using TileWidth but TiffDecompressorsFactory.Create constructs T4, T6, and Modified Huffman decompressors using the full frame width. TiffDecoderCore.DecodeTilesChunky can therefore direct frame-width fax scanlines into a tile-width buffer when TileWidth is smaller than ImageWidth. The mismatch causes attacker-controlled out-of-bounds writes, heap corruption, and process termination even with legal per-row run codes. This tiled-path vulnerability is distinct from oversized CCITT runs in strip decoding. This issue is fixed in version 4.1.1.
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Analysis
by VulDB Data Team • 10/06/2026
The ImageSharp library serves as a widely adopted open-source solution for image processing within the .NET ecosystem, providing capabilities for reading and writing various raster graphics formats including TIFF. A critical security vulnerability was identified in versions ranging from 3.0.0 through 4.1.1 concerning the handling of tiled Tagged Image File Format files. This flaw specifically affects the decoding process when a TIFF image is structured with tiles rather than strips, which is a common optimization for large images to allow parallel processing and efficient memory access patterns. The vulnerability stems from an inconsistency in how buffer dimensions are calculated versus how decompression parameters are initialized during the parsing of tiled chunks.
The technical root cause lies in a mismatch between the destination buffer allocation logic and the source data decomposition configuration within the TiffDecompressorsFactory class. When decoding a tiled TIFF, the system correctly allocates a destination buffer based on TileWidth, which represents the width of individual image tiles. However, when constructing decompressors for CCITT Group 3 (T4), CCITT Group 4 (T6), and Modified Huffman compression methods, the factory incorrectly utilizes ImageWidth, representing the full horizontal dimension of the entire frame, to configure internal state or buffer expectations within these decompressor instances. This architectural inconsistency means that while memory is reserved only for a single tile's width, the decompression engine operates under the assumption it can write up to the full image width into its output stream.
During execution, the TiffDecoderCore.DecodeTilesChunky method processes each tile by invoking the configured decompressors. Because the decompressor believes it has access to a buffer of ImageWidth but is actually writing into a buffer sized TileWidth, any tile where TileWidth is strictly less than ImageWidth results in an out-of-bounds write condition. The attacker can control this scenario by providing a maliciously crafted TIFF file that specifies tiles narrower than the total image width. As the decompressor processes scanlines and run codes, it writes pixel data beyond the allocated memory boundaries of the tile buffer. This leads to heap corruption as adjacent memory structures are overwritten with invalid or arbitrary data derived from the input file.
The operational impact of this vulnerability is severe, encompassing both denial of service and potential remote code execution vectors depending on the context in which ImageSharp is deployed. In many cases, particularly within web applications processing user-uploaded images, the immediate result is process termination due to access violations or heap corruption detected by memory managers. This constitutes a Denial of Service attack where an attacker can crash the hosting application simply by uploading a specific malformed image file. However, because the vulnerability involves arbitrary write operations in managed code environments that may interact with unmanaged resources or rely on precise object layouts for security checks, it also presents risks associated with heap exploitation techniques. These could potentially allow an attacker to achieve remote code execution if other mitigating factors are absent and the memory layout permits control flow hijacking through crafted run codes and tile structures.
This vulnerability is distinct from issues related to oversized CCITT runs in strip decoding because it specifically exploits the tiled image structure rather than simple row-based compression limits. The attack surface requires the victim application to decode a TIFF file that utilizes tiling, which might be less common than standard strip-encoded images but remains prevalent in professional imaging workflows and document storage systems. The flaw persists regardless of whether the input data contains legal per-row run codes; even validly encoded image data triggers the buffer overflow due to the fundamental dimension mismatch in the library's internal logic rather than malformed compression streams themselves.
To mitigate this risk, organizations using ImageSharp must upgrade immediately to version 4.1.1 or later, where the TiffDecompressorsFactory has been corrected to use TileWidth consistently for constructing decompressor instances that operate on tiled data. For applications unable to update promptly due to dependency constraints, input validation strategies should be implemented at the application layer to reject TIFF files with tile configurations that do not align with expected dimensions or to limit the maximum allowable image width and tile size combinations. Additionally, deploying runtime protection mechanisms such as heap hardening features available in modern .NET runtimes can help detect and prevent exploitation attempts arising from memory corruption events before they lead to code execution.
From a classification perspective, this vulnerability maps directly to CWE-787: Out-of-bounds Write, as the core issue is writing data beyond the allocated buffer boundary due to incorrect size calculations. It also aligns with CWE-120: Buffer Copy without Checking Size of Input in C/C++ concepts, adapted here for managed code memory management errors. In terms of adversarial tactics, this falls under ATT&CK technique T1568.002: Dynamic Resolution, where attackers use domain fronting or similar techniques to evade detection, though more accurately it represents a generic exploitation vector often seen in the initial access phase via malicious file uploads (T1566.001). The specific mechanism of exploiting memory corruption through crafted input files is characteristic of many high-severity vulnerabilities found in media parsing libraries and requires rigorous fuzzing and static analysis to detect during development cycles.