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NettyApplication

CVE-2026-56817

CRITICAL · 9.8 CVSS v3.1 Published 2026-07-21
Fix available
A fix is available. Upgrade to 4.1.136 / 4.2.16 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 4 weeks old

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 a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, any caller that can deliver bytes to a Netty channel pipeline containing `XmlDecoder` can send XML with a `DOCTYPE` declaration to an `AsyncXMLInputFactory` instantiated with no security configuration, leaving DTD and entity handling active depending on Aalto XML async parser behavior and creating conditional XML external entity risk. This issue is fixed in versions 4.1.136.Final and 4.2.16.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 XmlDecoder contains an XXE vulnerability where an AsyncXMLInputFactory is instantiated without security configuration, leaving DTD and entity processing enabled. Attackers who can send bytes to a channel pipeline with XmlDecoder can send XML with DOCTYPE declarations to trigger external entity processing, leading to potential SSRF, file disclosure, or denial of service.

MitigationUpgrade Netty to version 4.1.136.Final or 4.2.16.Final, or explicitly configure AsyncXMLInputFactory with security settings to disable DTD and external entities.

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:>= 4.1.0, < 4.1.136>= 4.2.0, < 4.2.16

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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
    Check your project dependencies (Maven pom.xml, Gradle build.gradle, or the netty-all.jar file manifest) for the exact Netty version. Look for netty.version property or direct netty-all dependency.
    Affected if The version is 4.1.0 through 4.1.135 inclusive, or 4.2.0 through 4.2.15 inclusive.
  2. Locate XmlDecoder in channel pipeline
    Search your codebase for XmlDecoder instantiation. Look for lines like 'pipeline.addLast(new XmlDecoder())' or similar patterns where XmlDecoder is added to a ChannelPipeline. Also search for any custom XmlDecoder implementations.
    Affected if XmlDecoder is present in any Netty channel pipeline that handles untrusted input.
  3. Verify if AsyncXMLInputFactory has security configuration
    Search the codebase for any configuration of AsyncXMLInputFactory or XMLInputFactory that is passed to XmlDecoder. Look for settings such as setProperty calls to disable DTDs (XMLConstants.ACCESS_EXTERNAL_DTD, XMLConstants.ACCESS_EXTERNAL_SCHEMA) or disable external entities. Also check if a custom XmlReader or parser is provided with secure settings.
    Affected if No secure configuration is found, or the AsyncXMLInputFactory is left with default (insecure) settings that allow DTD and external entity processing.
  4. Confirm XML processing of untrusted data
    Review how data flows into the XmlDecoder. Determine if the channel pipeline receiving XmlDecoder input is exposed to untrusted network sources, API endpoints, or message queues. Check if the data source can be controlled by external users or untrusted systems.
    Affected if The pipeline with XmlDecoder processes XML from untrusted or externally accessible sources.

You are affected if you run Netty 4.1.0-4.1.135 or 4.2.0-4.2.15, use XmlDecoder in a pipeline handling untrusted XML, and have not configured the AsyncXMLInputFactory with secure settings to disable DTD and external entity processing.

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 4.1.136 / 4.2.16 or later
Fixed in 4.1.1364.2.16
Interim mitigation

Upgrade Netty to version 4.1.136.Final or 4.2.16.Final, or explicitly configure AsyncXMLInputFactory with security settings to disable DTD and external entities.

Recommended fix High confidence

4.1.136.Final or 4.2.16.Final (depending on which branch is in use)

  1. Identify the current Netty version in use by examining project dependencies (e.g., pom.xml, build.gradle, or equivalent)
  2. If using Netty 4.1.x series: upgrade netty-all to version 4.1.136.Final
  3. If using Netty 4.2.x series: upgrade netty-all to version 4.2.16.Final
  4. Rebuild the project and verify no compilation errors
  5. Run existing tests to ensure no regressions
  6. Deploy and monitor for正常运行

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

Fix this in Netty Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-56817 in production — separate from our analysis above.

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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