GMS-2023-1796: PocketMine-MP vulnerable to server crash using badly formatted sign NBT in BlockActorDataPacket
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]: pocketminebt\UnexpectedTagTypeException: "Expected a tag of type pocketminebt\tag\CompoundTag, got pocketminebt\tag\ByteTag" (EXCEPTION) in "pmsrc/vendor/pocketmine/nbt/src/tag/CompoundTag" at line 107
--- Stack trace ---
#0 pmsrc/src/network/mcpe/handler/InGamePacketHandler(751): pocketminebt\tag\CompoundTag->getCompoundTag(string[9] FrontText)
#1 pmsrc/vendor/pocketmine/bedrock-protocol/src/BlockActorDataPacket(50): pocketmineetwork\mcpe\handler\InGamePacketHandler->handleBlockActorData(object pocketmineetwork\mcpe\protocol\BlockActorDataPacket#220241)
#2 pmsrc/src/network/mcpe/NetworkSession(433): pocketmineetwork\mcpe\protocol\BlockActorDataPacket->handle(object pocketmineetwork\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
.
References
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