GHSA-pggp-6c3x-2xmx Snappier has an infinite loop during SnappyStream decompression with malformed framed input

• NuGet Snappier: < 1.3.1 → fixed in 1.3.1

Summary `Snappier.SnappyStream` enters an uncatchable infinite loop when decompressing a malformed framed-format Snappy stream as small as 15 bytes. Details The hang manifests as a userspace busy loop with SnappyStreamDecompressor.Decompress repeatedly calling Crc32CAlgorithm.Append. The exact non-terminating loop in or above Decompress has not been traced further. PoC ```csharp using System.IO.Compression; using Snappier; byte[] data = { 0x00, 0x04, 0x00, 0x00, 0x64, 0x4e, 0x6c, 0x71, 0x79, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64 }; using var src = new MemoryStream(data); using var snap = new SnappyStream(src, CompressionMode.Decompress); using var dst = new MemoryStream(); snap.CopyTo(dst); // never returns ``` Impact A caller using `SnappyStream` on attacker-controlled bytes can be made to spin forever and burn a thread until the process is killed. `try/catch` around the stream operation can't recover (no exception is thrown).