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CVE-2026-44248

Netty: Resource exhaustion in MqttDecoder

CVSS 3.1 5.3 MEDIUMCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-44248

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-44248

Published

netty

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "netty",
                    "product": "netty",
                    "versions": [
                        {
                            "version": ">= 4.2.0.Alpha1, < 4.2.13.Final",
                            "status": "affected"
                        },
                        {
                            "version": "< 4.1.133.Final",
                            "status": "affected"
                        }
                    ]
                }

netty-codec-mqtt

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "io.netty",
                    "product": "netty-codec-mqtt",
                    "versions": [
                        {
                            "version": ">= 4.2.0.Alpha1, < 4.2.13.Final",
                            "status": "affected"
                        },
                        {
                            "version": "< 4.1.133.Final",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON