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Add checks, if enough data is present when reading PNG text chunks #3081

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Merged
JimBobSquarePants merged 6 commits into from
Mar 11, 2026
Merged

Add checks, if enough data is present when reading PNG text chunks #3081

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ba01f9c
Add check in ReadCompressedTextChunk() for enough data after keyword end
brianpopow Mar 10, 2026
eab4147
Add test case for not enough data after keyword end
brianpopow Mar 10, 2026
fca50b9
Add check for enough data in ReadInternationalTextChunk()
brianpopow Mar 10, 2026
457436d
Add test case for not enough data reading InternationalText chunk
brianpopow Mar 10, 2026
52c74b5
Add check, if translatedKeywordLength is < 0
brianpopow Mar 10, 2026
8d78fe0
Add test case for truncated data after language tag
brianpopow Mar 10, 2026
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25 changes: 20 additions & 5 deletions src/ImageSharp/Formats/Png/PngDecoderCore.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1402,26 +1402,31 @@ private void ReadCompressedTextChunk(ImageMetadata baseMetadata, PngMetadata met
return;
}

int zeroIndex = data.IndexOf((byte)0);
if (zeroIndex is < PngConstants.MinTextKeywordLength or > PngConstants.MaxTextKeywordLength)
int keywordEnd = data.IndexOf((byte)0);
if (keywordEnd is < PngConstants.MinTextKeywordLength or > PngConstants.MaxTextKeywordLength)
{
return;
}

byte compressionMethod = data[zeroIndex + 1];
if (keywordEnd < 0 || keywordEnd + 2 > data.Length)
{
return; // Not enough data for keyword + null + compression method.
}

byte compressionMethod = data[keywordEnd + 1];
if (compressionMethod != 0)
{
// Only compression method 0 is supported (zlib datastream with deflate compression).
return;
}

ReadOnlySpan<byte> keywordBytes = data[..zeroIndex];
ReadOnlySpan<byte> keywordBytes = data[..keywordEnd];
if (!TryReadTextKeyword(keywordBytes, out string name))
{
return;
}

ReadOnlySpan<byte> compressedData = data[(zeroIndex + 2)..];
ReadOnlySpan<byte> compressedData = data[(keywordEnd + 2)..];

if (this.TryDecompressTextData(compressedData, PngConstants.Encoding, out string? uncompressed)
&& !TryReadTextChunkMetadata(baseMetadata, name, uncompressed))
Expand Down Expand Up @@ -1932,6 +1937,11 @@ private void ReadInternationalTextChunk(ImageMetadata metadata, ReadOnlySpan<byt
return;
}

if (zeroIndexKeyword < 0 || zeroIndexKeyword + 4 > data.Length)
{
return; // Not enough data for keyword + null + flag + method + language.
}

byte compressionFlag = data[zeroIndexKeyword + 1];
if (compressionFlag is not (0 or 1))
{
Expand All @@ -1956,6 +1966,11 @@ private void ReadInternationalTextChunk(ImageMetadata metadata, ReadOnlySpan<byt

int translatedKeywordStartIdx = langStartIdx + languageLength + 1;
int translatedKeywordLength = data[translatedKeywordStartIdx..].IndexOf((byte)0);
if (translatedKeywordLength < 0)
{
return;
}

string translatedKeyword = PngConstants.TranslatedEncoding.GetString(data.Slice(translatedKeywordStartIdx, translatedKeywordLength));

ReadOnlySpan<byte> keywordBytes = data[..zeroIndexKeyword];
Expand Down
69 changes: 69 additions & 0 deletions tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.Chunks.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,75 @@ public void Decode_TruncatedPhysChunk_ExceptionIsThrown()
Assert.Equal("pHYs chunk is too short", exception.Message);
}

// https://github.com/SixLabors/ImageSharp/issues/3079
[Fact]
public void Decode_CompressedTxtChunk_WithTruncatedData_DoesNotThrow()
{
byte[] payload = [137, 80, 78, 71, 13, 10, 26, 10, // PNG signature
0, 0, 0, 13, // chunk length 13 bytes
73, 72, 68, 82, // chunk type IHDR
0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, // data
55, 110, 249, 36, // checksum
0, 0, 0, 2, // chunk length
122, 84, 88, 116, // chunk type zTXt
1, 0, // truncated data
100, 138, 166, 20, // crc
0, 0, 0, 10, // chunk length 10 bytes
73, 68, 65, 84, // chunk type IDAT
120, 1, 99, 96, 0, 0, 0, 2, 0, 1, // data
115, 117, 1, 24, // checksum
0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130]; // end chunk

using MemoryStream stream = new(payload);
using Image<Rgba32> image = Image.Load<Rgba32>(stream);
}

// https://github.com/SixLabors/ImageSharp/issues/3079
[Fact]
public void Decode_InternationalText_WithTruncatedData_DoesNotThrow()
{
byte[] payload = [137, 80, 78, 71, 13, 10, 26, 10, // PNG signature
0, 0, 0, 13, // chunk length 13 bytes
73, 72, 68, 82, // chunk type IHDR
0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, // data
55, 110, 249, 36, // checksum
0, 0, 0, 2, // chunk length
105, 84, 88, 116, // chunk type iTXt
1, 0, // truncated data
225, 200, 214, 33, // crc
0, 0, 0, 10, // chunk length 10 bytes
73, 68, 65, 84, // chunk type IDAT
120, 1, 99, 96, 0, 0, 0, 2, 0, 1, // data
115, 117, 1, 24, // checksum
0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130]; // end chunk

using MemoryStream stream = new(payload);
using Image<Rgba32> image = Image.Load<Rgba32>(stream);
}

// https://github.com/SixLabors/ImageSharp/issues/3079
[Fact]
public void Decode_InternationalText_WithTruncatedDataAfterLanguageTag_DoesNotThrow()
{
byte[] payload = [137, 80, 78, 71, 13, 10, 26, 10, // PNG signature
0, 0, 0, 13, // chunk length 13 bytes
73, 72, 68, 82, // chunk type IHDR
0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, // data
55, 110, 249, 36, // checksum
0, 0, 0, 21, // chunk length
105, 84, 88, 116, // chunk type iTXt
73, 110, 116, 101, 114, 110, 97, 116, 105, 111, 110, 97, 108, 50, 0, 0, 0, 114, 117, 115, 0, // truncated data after language tag
225, 200, 214, 33, // crc
0, 0, 0, 10, // chunk length 10 bytes
73, 68, 65, 84, // chunk type IDAT
120, 1, 99, 96, 0, 0, 0, 2, 0, 1, // data
115, 117, 1, 24, // checksum
0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130]; // end chunk

using MemoryStream stream = new(payload);
using Image<Rgba32> image = Image.Load<Rgba32>(stream);
}

private static string GetChunkTypeName(uint value)
{
byte[] data = new byte[4];
Expand Down
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