Summary A player sending a packet can cause the server to crash by providing incorrect sign data in NBT in "BlockActorDataPacket". Details This vulnerability was discovered using the "BlockActorDataPacket", but other packets may also be affected. The player would seem to just need to send an NBT with an incorrect type to throw this error. [Server thread/CRITICAL]: pocketmine\nbt\UnexpectedTagTypeException: "Expected a tag of type pocketmine\nbt\tag\CompoundTag, got pocketmine\nbt\tag\ByteTag" (EXCEPTION) in "pmsrc/vendor/pocketmine/nbt/src/tag/CompoundTag" at line 107 --- Stack trace --- #0 pmsrc/src/network/mcpe/handler/InGamePacketHandler(751): pocketmine\nbt\tag\CompoundTag->getCompoundTag(string[9] FrontText) #1 pmsrc/vendor/pocketmine/bedrock-protocol/src/BlockActorDataPacket(50): pocketmine\network\mcpe\handler\InGamePacketHandler->handleBlockActorData(object pocketmine\network\mcpe\protocol\BlockActorDataPacket#220241) #2 pmsrc/src/network/mcpe/NetworkSession(433): pocketmine\network\mcpe\protocol\BlockActorDataPacket->handle(object pocketmine\network\mcpe\handler\InGamePacketHandler#190572) PoC Use a bot or proxy to send a packet when editing a sign. This packet should contain an NBT with incorrect types but correct architecture. Impact This makes it possible to shutdown a server for someone who knows how to operate it. As this was discovered in 4.22.1, everyone with at least this version is affected. Patches This bug was fixed by 0c250a2ef09627b48aa52302f6cc7e1f2afb70ea in the 4.22.3 and 5.2.1 releases. Workarounds A plugin may be able to handle "DataPacketReceiveEvent" for "BlockActorDataPacket", and verify that the "FrontText" tag is a "TAG_Compound".