CVE-2026-44248 — Netty: Resource exhaustion in MqttDecoder

Description (CNA)

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, the MQTT 5 header Properties section is parsed and buffered before any message size limit is applied. Specifically, in MqttDecoder, the decodeVariableHeader() method is called before the bytesRemainingBeforeVariableHeader > maxBytesInMessage check. The decodeVariableHeader() can call other methods which will call decodeProperties(). Effectively, Netty does not apply any limits to the size of the properties being decoded. Additionally, because MqttDecoder extends ReplayingDecoder, Netty will repeatedly re-parse the enormous Properties sections and buffer the bytes in memory, until the entire thing parses to completion. This can cause high resource usage in both CPU and memory. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Affected (CNA)

Vendor / product	Versions
netty / netty	affected >= 4.2.0.Alpha1, < 4.2.13.Final; affected < 4.1.133.Final
io.netty / netty-codec-mqtt	affected >= 4.2.0.Alpha1, < 4.2.13.Final; affected < 4.1.133.Final

CWE

CWE-400

References

https://github.com/netty/netty/security/advisories/GHSA-jfg9-48mv-9qgx

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A flaw was found in Netty, an asynchronous event-driven network application framework. A remote attacker can exploit this vulnerability by sending a crafted MQTT 5 header with an oversized Properties section. This causes Netty to repeatedly parse and buffer the large Properties section in memory before any message size limits are applied, leading to high CPU and memory consumption. This can result in a Denial of Service (DoS) condition, making the affected system unavailable.