CVE-2026-56818: Netty · RedisArrayAggregator max-elements failure leaves retained partial aggregate state

## 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 `RedisArrayAggregatorIncompleteCleanupPovTest.java` under: `codec-redis/src/test/java/io/netty/handler/codec/redis/` Run: ```fish ./mvnw -pl codec-redis -am -Dtest=RedisArrayAggregatorIncompleteCleanupPovTest -Dsurefire.failIfNoSpecifiedTests=false -DskipNativeTests -DskipAutobahnTests test ``` The test suite includes: - serialized RESP trigger through `RedisDecoder`, `RedisBulkStringAggregator`, and `RedisArrayAggregator`; - direct refcount proof that max-elements overflow does not release the retained child immediately; - post-exception continuation proof that the stale aggregate consumes a later message; - nested-depth controls that clear the same partial aggregate state. All five tests pass on current `4.2`, `4.2.15.Final`, and `4.1.135.Final`. ## Impact For Redis codec pipelines that continue after codec exceptions, an unauthenticated peer can keep attacker-controlled aggregate state alive across a security-limit exception. This can pin retained pooled buffers until channel close/removal or until a later message completes the stale aggregate. `RedisBulkStringAggregator` permits bulk strings up to `RedisConstants.REDIS_MESSAGE_MAX_LENGTH` (`512MB`), so the retained child can be large in deployments that aggregate untrusted Redis streams. Applications that always close the channel or remove the handler on decoder exceptions will trigger existing cleanup; the issue is the missing immediate cleanup on the max-elements failure path while the handler remains installed. ## Suggested Fix Call `releaseAndClearDepths()` before throwing from the max-elements branch. Consider applying the same cleanup to all unrecoverable `decodeRedisArrayHeader(...)` error exits that can occur while `depths` is non-empty. ## Affected Package/Versions `io.netty:netty-codec-redis` Confirmed on: - current `4.2` branch head `7bae566a93e69409697fe57fa807910ba5c9720e` - `4.2.15.Final` at `a41f7b289ce1` - `4.1.135.Final` at `f05f765d8146` ## Advisory History This differs from the public Redis codec advisories because it reproduces on their patched tags: - `GHSA-5w86-c3rq-vjj7` - `GHSA-3244-j874-rhc2` / `CVE-2026-44250` - `GHSA-6jv9-x5w9-2ccm` / `CVE-2026-48006` - `GHSA-6ghj-frrj-jjj3` / `CVE-2026-44890` ## Why This Is Not Intended Behavior The public API docs document `RedisArrayAggregator` as aggregating `RedisMessage` parts into `ArrayRedisMessage` and document a `CodecException` when an array header exceeds `maxElements`. They do not document preserving pre-exception partial aggregate state after that limit fires. The adjacent nested-depth branch already calls `releaseAndClearDepths()` before throwing. The max-elements branch is the sibling aggregation-limit branch but throws without cleanup. Netty's later Redis lifecycle cleanup patch explicitly added release behavior for nested-array failure and handler removal, leaving the max-elements failure branch as a missed cleanup path.

• github.com/netty/netty/security/advisories/GHSA-p9jm-q85p-7mcp (opens in a new tab)
• github.com/netty/netty/pull/17065 (opens in a new tab)
• github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b (opens in a new tab)
• github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6 (opens in a new tab)
• github.com/netty/netty (opens in a new tab)

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