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CVE-2026-44248 medium CVSS 5.3

Vulnerability in io.netty:netty-codec-mqtt (CVE-2026-44248)

Summary

Vulnerability in io.netty:netty-codec-mqtt (CVE-2026-44248). Risk of unauthorized operations or information disclosure. Exploitable via MqttDecoder. Mitigation: upgrade to 4.1.133.Final or later.

Original description

The description as published by the source.

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

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-44248 has been found in io.netty:netty-codec-mqtt.
Attackers can target a specific entry point like MqttDecoder over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade io.netty:netty-codec-mqtt to 4.1.133.Final or later.
If unsure, ask your IT team or search "io.netty:netty-codec-mqtt CVE-2026-44248" on the vendor's site.

CVE-2026-44248 (io.netty:netty-codec-mqtt) — CWE-400 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: MqttDecoder / ReplayingDecoder
Patched: 4.1.133.Final — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-400) exists in io.netty:netty-codec-mqtt. Attackers reach the vulnerable code path via MqttDecoder without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of io.netty:netty-codec-mqtt. Attack surface: MqttDecoder / ReplayingDecoder.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 4.1.133.Final.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで io.netty:netty-codec-mqtt を使っているサービスとバージョンを洗い出す。

  2. 2
    Apply patch patch 
    Upgrade io.netty:netty-codec-mqtt to 4.1.133.Final

    ステージング環境で 4.1.133.Final に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Maven io.netty:netty-codec-mqtt
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.1.133.Final"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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