Book page text, count, and author/title length is not limited in PocketMine-MP

Summary

### Impact Players can fill book pages with as many characters as they like; the server does not check this. In addition, the maximum of 50 pages is also not enforced, meaning that players can create "book bombs". This causes a variety of problems: - Oversized NBT on the wire costing excess bandwidth for server and client - Server crashes when saving region-based worlds due to exceeding maximum chunk size of 1 MB (PM3-specific) - Server crashes if any book page exceeds 32 KiB (due to TAG_String size limit) (PM4-specific) This does, however, require that an attacker obtain a writable book in the first place in order to exploit the problem. ### Patches The bug has been fixed in 3.26.5 and 4.0.5. ### Workarounds Ban writable books, or use a plugin to cancel `PlayerEditBookEvent` to cancel the event if `strlen(text) > 1024 || mb_strlen(text) > 256`. ### For more information If you have any questions or comments about this advisory: * Email us at [[email protected]](mailto:[email protected])