PT-2026-38399 · Maven · Io.Netty:Netty-Codec-Mqtt

Published 2026-05-07 · Updated 2026-05-07 · CVE-2026-44248

OSV

CVSS v3.1

5.3

Medium

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Impact

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.

Resources

ANT-2026-09608 https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html# Toc3901027

Fix

Resource Exhaustion

Weakness Enumeration

CWE-400

Related Identifiers

CVE-2026-44248

GHSA-JFG9-48MV-9QGX

Affected Products

Io.Netty:Netty-Codec-Mqtt

References · 4

• https://osv.dev/vulnerability/GHSA-jfg9-48mv-9qgx · Vendor Advisory
• https://github.com/netty/netty · Note
• https://github.com/netty/netty/security/advisories/GHSA-jfg9-48mv-9qgx · Note
• https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901027 · Note