CVE-2026-44248
MEDIUMCVE-2026-44248 is a medium-severity (CVSS 5.3) vulnerability in io.netty:netty-codec-mqtt. O3 Security confirms whether CVE-2026-44248 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Netty: Resource exhaustion in MqttDecoder
Real-World Exposure
io.netty:netty-codec-mqtt☕io.netty:netty-codec-mqttReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-mqtt | ≥ 4.2.0.Alpha1&&< 4.2.13.Final | 4.2.13.Final |
| ☕Maven | io.netty:netty-codec-mqtt | all versions | 4.1.133.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-mqtt. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update io.netty:netty-codec-mqtt to 4.2.13.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44248 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-44248 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-44248. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-44248 in your dependencies?
O3 detects CVE-2026-44248 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.