GMS-2022-4: Book page text, count, and author/title length is not limited in PocketMine-MP

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 team@pmmp.io