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Handle vendor-specific and malformed ZIP extra fields safely #972

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Merged
adamhathcock merged 1 commit into from
Oct 25, 2025
Merged

Handle vendor-specific and malformed ZIP extra fields safely #972

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21 changes: 19 additions & 2 deletions src/SharpCompress/Common/Zip/Headers/ZipFileEntry.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,8 +91,15 @@ internal PkwareTraditionalEncryptionData ComposeEncryptionData(Stream archiveStr

protected void LoadExtra(byte[] extra)
{
for (var i = 0; i < extra.Length - 4; )
for (var i = 0; i < extra.Length; )
{
// Ensure we have at least a header (2-byte ID + 2-byte length)
if (i + 4 > extra.Length)
{
// Incomplete header — stop parsing extras
break;
}

var type = (ExtraDataType)BinaryPrimitives.ReadUInt16LittleEndian(extra.AsSpan(i));
if (!Enum.IsDefined(typeof(ExtraDataType), type))
{
Expand All @@ -106,7 +113,17 @@ protected void LoadExtra(byte[] extra)
if (length > extra.Length)
{
// bad extras block
return;
break; // allow processing optional other blocks
}
// Some ZIP files contain vendor-specific or malformed extra fields where the declared
// data length extends beyond the remaining buffer. This adjustment ensures that
// we only read data within bounds (i + 4 + length <= extra.Length)
// The example here is: 41 43 18 00 41 52 43 30 46 EB FF FF 51 29 03 C6 03 00 00 00 00 00 00 00 00
// No existing zip utility uses 0x4341 ('AC')
if (i + 4 + length > extra.Length)
{
// incomplete or corrupt field
break; // allow processing optional other blocks
}

var data = new byte[length];
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6 changes: 3 additions & 3 deletions src/SharpCompress/packages.lock.json
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Original file line number Diff line number Diff line change
Expand Up @@ -335,9 +335,9 @@
"net8.0": {
"Microsoft.NET.ILLink.Tasks": {
"type": "Direct",
"requested": "[8.0.17, )",
"resolved": "8.0.17",
"contentHash": "x5/y4l8AtshpBOrCZdlE4txw8K3e3s9meBFeZeR3l8hbbku2V7kK6ojhXvrbjg1rk3G+JqL1BI26gtgc1ZrdUw=="
"requested": "[8.0.21, )",
"resolved": "8.0.21",
"contentHash": "s8H5PZQs50OcNkaB6Si54+v3GWM7vzs6vxFRMlD3aXsbM+aPCtod62gmK0BYWou9diGzmo56j8cIf/PziijDqQ=="
},
"Microsoft.SourceLink.GitHub": {
"type": "Direct",
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