Netty is an asynchronous, event-driven network application framework. Prior to 4.1.136.Final and 4.2.16.Final, the RedisArrayAggregator Redis codec clears retained partial aggregate state when the maxNestedArrayDepth limit is exceeded, but it does not clear the same state when the sibling maxElements limit is exceeded. A peer can start a valid RESP array, send a bulk string child, then send a nested array header longer than the configured maxElements. Netty throws a decoder exception in decodeRedisArrayHeader, but the existing partial aggregate remains retained in the handler. If the application leaves the channel alive after the exception, later messages are still consumed into the pre-error aggregate, allowing an unauthenticated peer to keep attacker-controlled aggregate state alive across a security-limit exception and pin retained pooled buffers. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Affected: Maven: io.netty:netty-codec-redis

## Summary

`RedisArrayAggregator` clears retained partial aggregate state when the `maxNestedArrayDepth` limit is exceeded, but it does not clear the same state when the sibling `maxElements` limit is exceeded. A peer can start a valid RESP array, send a bulk-string child, then send a nested array header longer than the configured `maxElements`. Netty throws a decoder exception, but the existing partial aggregate remains retained in the handler.

If the application leaves the channel alive after the exception, later messages are still consumed into the pre-error aggregate. The supplied PoV proves both the retained `ByteBuf` reference and the stale parser state continuation.

## Technical Details

`RedisArrayAggregator.decode(...)` retains non-array messages before adding them to `depths.peek().children`. In `decodeRedisArrayHeader(...)`, the `header.length() > maxElements` branch throws immediately:

```java if (header.length() > maxElements) { throw new CodecException("this codec doesn't support longer length than " + maxElements); } ```

The immediately following nested-depth branch clears retained aggregate state before throwing:

```java if (depths.size() >= maxNestedArrayDepth) { releaseAndClearDepths(); throw new CodecException("max nested array depth exceeded: " + maxNestedArrayDepth); } ```

The missing cleanup in the first branch leaves retained children and aggregate state reachable after the exception.

## PoC

Place the supplied `RedisArrayAggregator…

netty-4.1.136-1.1 on GA media

Affected: Ubuntu:Pro:14.04:LTS: netty, Ubuntu:Pro:16.04:LTS: netty, Ubuntu:Pro:18.04:LTS: netty, Ubuntu:Pro:20.04:LTS: netty, Ubuntu:Pro:22.04:LTS: netty, Ubuntu:Pro:24.04:LTS: netty, Ubuntu:Pro:26.04:LTS: netty

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.136.Final and 4.2.16.Final, the RedisArrayAggregator Redis codec clears retained partial aggregate state when the maxNestedArrayDepth limit is exceeded, but it does not clear the same state when the sibling maxElements limit is exceeded. A peer can start a valid RESP array, send a bulk string child, then send a nested array header longer than the configured maxElements. Netty throws a decoder exception in decodeRedisArrayHeader, but the existing partial aggregate remains retained in the handler. If the application leaves the channel alive after the exception, later messages are still consumed into the pre-error aggregate, allowing an unauthenticated peer to keep attacker-controlled aggregate state alive across a security-limit exception and pin retained pooled buffers. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Netty ausnutzen, um einen Denial of Service Angriff durchzuführen.