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Vulnerability · Published May 13, 2026 · Assigned by GitHub_M

CVE-2026-44248Netty: Resource exhaustion in MqttDecoder

Medium 5.3

In plain English

A medium-severity uncontrolled resource consumption in netty-codec-mqtt from io.netty. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 47% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.6%top 53.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12nettyno fix listedDEBIAN-CVE-2026-44248
Debian:13nettyno fix listedDEBIAN-CVE-2026-44248
Debian:14nettyno fix listedDEBIAN-CVE-2026-44248
Mavenio.netty:netty-codec-mqtt4.2.13.FinalGHSA-jfg9-48mv-9qgx
Mavenio.netty:netty-codec-mqtt4.1.133.FinalGHSA-jfg9-48mv-9qgx
Ubuntu:25.10nettyno fix listedUBUNTU-CVE-2026-44248

Affected products (as reported)

VendorProductVersions
netty netty >= 4.2.0.Alpha1, < 4.2.13.Final< 4.1.133.Final
io.netty netty-codec-mqtt >= 4.2.0.Alpha1, < 4.2.13.Final< 4.1.133.Final

Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References