PocketMine-MP before 3.26.5 and 4.0.x before 4.0.5 does not limit book page text length, page count, or author/title length. A player who obtains a writable book can create oversized NBT ('book bombs'), causing excess bandwidth consumption and server crashes (exceeding the 1 MB chunk size limit when saving region-based worlds in PM3, or exceeding the 32 KiB TAGString limit in PM4).

PocketMine-MP before 4.0.7 contains an unhandled exception vulnerability in the ModalFormResponsePacket handler when processing malformed JSON from clients. Attackers can send specially crafted form response packets with invalid JSON to trigger an uncaught InvalidArgumentException, causing server crashes.

PocketMine-MP before 4.2.10 fails to validate the total length of incoming chat message blobs before splitting them by newline characters, allowing attackers to send large messages containing many newlines. Malicious clients can send megabyte-sized chat packets and bombard the server with thousands of such messages, causing server lockups lasting seconds or minutes.