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Prevent crafted DOS attack. #2501

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merged 1 commit into from
Aug 10, 2023
Merged

Prevent crafted DOS attack. #2501

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2 changes: 1 addition & 1 deletion src/ImageSharp/Formats/Pbm/BufferedReadStreamExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ public static void SkipWhitespaceAndComments(this BufferedReadStream stream)
{
innerValue = stream.ReadByte();
}
while (innerValue != 0x0a);
while (innerValue is not 0x0a and not -0x1);
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Should a similar check be added also in line 52 ?

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int current = stream.ReadByte() - 0x30;
if ((uint)current > 9)
{
    break;
}

In case of EOF current == -1 -0x30 == -0x31. (uint)-0x31 == SomeHighNum > 9.

Nevertheless, a test case might be nice, these infinite loops are dangerous. 💀

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Yeah, that's why I left it. We actually enter that loop in ReadDecimal with this test, but I'll double check before merging.

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We cover this code with the test so I'm happy. I'll open another PR after this one to backport the fix to 2.X


// Continue searching for whitespace.
val = innerValue;
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11 changes: 11 additions & 0 deletions tests/ImageSharp.Tests/Formats/Pbm/PbmMetadataTests.cs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using SixLabors.ImageSharp.Formats;
using SixLabors.ImageSharp.Formats.Pbm;
using static SixLabors.ImageSharp.Tests.TestImages.Pbm;

Expand Down Expand Up @@ -80,4 +81,14 @@ public void Identify_DetectsCorrectComponentType(string imagePath, PbmComponentT
Assert.NotNull(bitmapMetadata);
Assert.Equal(expectedComponentType, bitmapMetadata.ComponentType);
}

[Fact]
public void Identify_HandlesCraftedDenialOfServiceString()
{
byte[] bytes = Convert.FromBase64String("UDEjWAAACQAAAAA=");
ImageInfo info = Image.Identify(bytes);
Assert.Equal(default, info.Size);
Configuration.Default.ImageFormatsManager.TryFindFormatByFileExtension("pbm", out IImageFormat format);
Assert.Equal(format!, info.Metadata.DecodedImageFormat);
}
}