fkie_cve-2026-106118

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.

GHSA-v76p-62qx-wwq2 — ImageSharp: Tiled fax TIFF: tile buffer sized by TileWidth but fax decompressor writes scanlines of ImageWidth — heap O…

Affected: NuGet: ImageSharp

## Summary

When decoding a tiled TIFF with fax compression (T4/T6/MH), `DecodeTilesChunky` allocates each tile buffer from **TileWidth** (`ceil(TileWidth*bpp/8)*TileLength` bytes) but constructs the fax decompressor with **frame.Width**: `TiffDecompressorsFactory` ignores the `isTiled/tileWidth/tileHeight` parameters entirely. The T4/T6/MH decompressors treat the full image width as the scanline length and advance (and really write, via read-modify-write bit ops) `frame.Width` bits per row, with no bounds check against the tile buffer. The very first tile therefore writes linearly out of bounds — about `ImageWidth/8` bytes per row × TileLength rows into a `TileWidth`-sized buffer. With ImageWidth=4,000,000, TileWidth=16, TileLength=16 this writes ~2 MB past a 32-byte buffer and kills the process deterministically; a T6 all-white variant advances the bit offset by >512 MB silently, showing an alarm-free heap-corruption window for the same defect. A crafted file fully controls the OOB length per tile and works with perfectly legal per-row run codes (no overlong runs needed).

Verified at commit `5cd4d0d26a82a9549f297a237aea9cf665bddff8` (main; latest release v4.1.0, the supported major).

## Details

Root cause: a size mismatch between tile buffer allocation and decompressor width, because the factory drops the tile parameters.

- Allocation: [TiffDecoderCore.cs#L792-L794](https://github.com/SixLabors/ImageSharp/blob/5cd4d0d26a82a9549f297a237aea9cf665bddff8/src/ImageSharp/For…

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fkie_cve-2026-106118

GHSA-v76p-62qx-wwq2 — ImageSharp: Tiled fax TIFF: tile buffer sized by TileWidth but fax decompressor writes scanlines of ImageWidth — heap O…