From c6540799e319919bbbea91f36f578f1cb517f7a3 Mon Sep 17 00:00:00 2001
From: Ynse Hoornenborg <github@ynse.nl>
Date: Mon, 10 Jan 2022 05:58:50 +0100
Subject: [PATCH] Zero out the iTxt header

---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index c428f52e4c..da6878051f 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -680,12 +680,21 @@ namespace SixLabors.ImageSharp.Formats.Png
                 return;
             }
 
-            int payloadLength = xmpData.Length + PngConstants.XmpKeyword.Length + 5;
+            int payloadLength = xmpData.Length + PngConstants.XmpKeyword.Length + iTxtHeaderSize;
             using (IMemoryOwner<byte> owner = this.memoryAllocator.Allocate<byte>(payloadLength))
             {
                 Span<byte> payload = owner.GetSpan();
                 PngConstants.XmpKeyword.CopyTo(payload);
-                int bytesWritten = PngConstants.XmpKeyword.Length + iTxtHeaderSize;
+                int bytesWritten = PngConstants.XmpKeyword.Length;
+
+                // Write the iTxt header (all zeros in this case)
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+
+                // And the XMP data itself
                 xmpData.CopyTo(payload.Slice(bytesWritten));
                 this.WriteChunk(stream, PngChunkType.InternationalText, payload);
             }