ImageSharp: CCITT fax decompression (T4/Modified Huffman): unbounded WriteBits overflows strip buffer — heap OOB write in SixLabors.ImageSharp

Summary When decoding a fax-compressed strip TIFF Compression=3 / Group 3 1D, or Compression=2 / Modified Huffman, the CCITT decompressors write decoded runs through BitWriterUtils.WriteBits/WriteBit/WriteZeroBit, which advance and write bits via Unsafe.Add with read-modify-write semantics —...