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NettyApplication

CVE-2026-42579

CRITICAL · 9.1 CVSS v3.1 Published 2026-05-13
Fix available
A fix is available. Upgrade to 4.1.133 / 4.2.13 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's DNS codec does not enforce RFC 1035 domain name constraints during either encoding or decoding. This creates a bidirectional attack surface: malicious DNS responses can exploit the decoder, and user-influenced hostnames can exploit the encoder. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Netty's DNS codec fails to enforce RFC 1035 domain name constraints during both encoding and decoding operations. This allows malformed domain names to be processed, creating a bidirectional attack surface where malicious DNS responses can exploit the decoder and user-influenced hostnames can exploit the encoder.

MitigationUpgrade Netty to version 4.2.13.Final or 4.1.133.Final or later to enforce proper RFC 1035 domain name validation in the DNS codec.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
NettyApplication
Affected:< 4.1.133>= 4.2.0, < 4.2.13

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Netty version in use
    Inspect your project's dependency management (pom.xml, build.gradle, package.json, or classpath). Search for io.netty:netty-all or specific Netty module dependencies and note the version number.
    Affected if The version is less than 4.1.133.Final or greater than or equal to 4.2.0 but less than 4.2.13.Final
  2. Confirm netty-codec-dns module is present
    Search your dependencies for io.netty:netty-codec-dns. This module contains the vulnerable DNS codec classes.
    Affected if The netty-codec-dns dependency exists in your project
  3. Check for DNS decoding usage
    Search your codebase for imports and usage of DnsMessageDecoder, DnsDatagramPacket, or DnsResponse classes. These indicate your code processes DNS responses.
    Affected if Code uses DNS response parsing or decoding classes
  4. Check for DNS encoding usage
    Search your codebase for usage of DnsMessageEncoder, DnsRecordEncoder, or direct construction of DnsQuery/DnsResponse objects with hostnames. These indicate your code encodes domain names.
    Affected if Code encodes DNS messages or domain names into wire format
  5. Inspect runtime classpath
    At runtime, inspect the Netty version loaded by the classloader: locate netty-common-.jar in your classpath and check the filename for the exact version, or run: java -cp $(find . -name 'netty-common*.jar' | head -1) io.netty.internal.VersionInfo.version()
    Affected if The runtime Netty version matches the affected ranges in step 1

You are affected if your Netty version is within 4.2.0 to 4.2.12.Final or below 4.1.133.Final AND you use the netty-codec-dns module to encode or decode DNS messages.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.1.133 / 4.2.13 or later
Fixed in 4.1.1334.2.13
Interim mitigation

Upgrade Netty to version 4.2.13.Final or 4.1.133.Final or later to enforce proper RFC 1035 domain name validation in the DNS codec.

Recommended fix High confidence

4.1.133.Final (for 4.1.x line) or 4.2.13.Final (for 4.2.x line)

  1. Identify the current Netty version in use by examining Maven pom.xml or Gradle build.gradle dependencies
  2. If using Netty 4.1.x line (version < 4.1.133), upgrade to 4.1.133.Final
  3. If using Netty 4.2.x line (version >= 4.2.0 and < 4.2.13), upgrade to 4.2.13.Final
  4. Update the dependency version in the build configuration file
  5. Run build and tests to verify compatibility
  6. Redeploy the updated application

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Netty Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,920
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,072.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42579 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data