CVE-2026-42582: Netty QpackDecoder Vulnerability Exposes Apps to DoS
The National Vulnerability Database has issued an advisory for CVE-2026-42582, impacting Netty, an asynchronous network application framework. The vulnerability exists in Netty versions prior to 4.2.13.Final, specifically within the QpackDecoder when handling HTTP/3 header blocks. A flaw in the decodeHuffmanEncodedLiteral function allows an attacker to craft a malicious string literal with an arbitrarily large length value.
This critical oversight means the application attempts to allocate a byte array of the specified, unverified length before checking if the corresponding data actually exists in the compressed field section. The wire encoding permits expressing an extremely large length using very few bytes. This can lead to excessive memory allocation requests, consuming system resources and triggering a denial-of-service (DoS) condition on the affected server.
The National Vulnerability Database rates this with a CVSS score of 7.5 (HIGH), categorizing it under CWE-770 (Improper Restriction of Resource from One-Time Operations) and CWE-789 (Uncontrolled Memory Allocation). The fix is available in Netty version 4.2.13.Final, and immediate patching is crucial for any application leveraging Netty for network communication.
What This Means For You
- If your applications or services rely on Netty, you are exposed to a remote denial-of-service attack. This isn't just a theoretical bug; an unauthenticated attacker can crash your service. You need to identify all instances of Netty in your environment and prioritize upgrading to version 4.2.13.Final or later immediately. Check your dependencies for Netty and push for patches.
Related ATT&CK Techniques
🛡️ Detection Rules
6 rules · 6 SIEM formats6 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Web Application Exploitation Attempt — CVE-2026-42582
title: Web Application Exploitation Attempt — CVE-2026-42582
id: scw-2026-05-13-1
status: experimental
level: high
description: |
Detects common exploitation patterns targeting web applications. Review CVE-2026-42582 advisories for specific indicators.
author: SCW Feed Engine (auto-generated)
date: 2026-05-13
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-42582/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: webserver
detection:
selection:
cs-uri-query|contains:
- '..'
- 'SELECT'
- 'UNION'
- '<script'
- 'cmd='
- '/etc/passwd'
condition: selection
falsepositives:
- Legitimate activity from CVE-2026-42582
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-42582 | Denial of Service | Netty framework versions prior to 4.2.13.Final |
| CVE-2026-42582 | Memory Corruption | io.netty.handler.codec.http3.QpackDecoder#decodeHuffmanEncodedLiteral |
| CVE-2026-42582 | Buffer Overflow | Lack of length validation (length <= in.readableBytes()) before new byte[length] in QpackDecoder |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 13, 2026 at 22:17 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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