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NettyApplication

CVE-2026-42581

CRITICAL · 9.8 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, HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. 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

In Netty's HttpObjectDecoder, a guard that strips conflicting Content-Length headers when Transfer-Encoding: chunked is present only existed for HTTP/1.1 messages. For HTTP/1.0 requests carrying both headers, the decoder processes the body as chunked but leaves Content-Length intact in the forwarded HttpMessage, causing downstream components that trust Content-Length over Transfer-Encoding to disagree on message boundaries and enabling HTTP request smuggling.

MitigationUpgrade Netty to version 4.2.13.Final or 4.1.133.Final or later, which includes the fix for this HTTP/1.0 request smuggling vulnerability.

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
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
    Examine your project's dependency management (Maven pom.xml, Gradle build.gradle, or runtime classpath) for the netty version (e.g., netty.version property or the netty-all / io.netty artifact version)
    Affected if The version is below 4.1.133 or between 4.2.0 and 4.2.12 inclusive
  2. Confirm HTTP/1.0 support is enabled
    Review your Netty pipeline initialization code for HttpServerCodec, HttpRequestDecoder, or HttpResponseDecoder instances configured with HttpObjectDecoder subclasses, and verify acceptHTTP10Requests is not explicitly disabled
    Affected if HTTP/1.0 requests are accepted by your Netty server (default behavior unless explicitly restricted to HTTP/1.1 only)
  3. Verify chunked transfer encoding handler
    Check if your Netty pipeline includes any chunked transfer handling such as ChunkedWriteHandler, or uses default chunked encoding support in the HTTP codecs
    Affected if Chunked transfer encoding handling is enabled (default in most Netty HTTP server configurations)
  4. Inspect for Content-Length and Transfer-Encoding conflict handling
    Analyze your Netty HttpObjectDecoder configuration or custom decoder subclass - look for any code that inspects or validates conflicting Content-Length and Transfer-Encoding headers in HTTP/1.0 requests
    Affected if Your decoder does not explicitly strip or reject conflicting Content-Length headers when Transfer-Encoding: chunked is present in HTTP/1.0 requests

You are affected if your Netty version falls in the vulnerable ranges (below 4.1.133 or between 4.2.0 and 4.2.12) AND your server accepts HTTP/1.0 requests with chunked transfer encoding enabled.

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, which includes the fix for this HTTP/1.0 request smuggling vulnerability.

Recommended fix High confidence

4.1.133.Final or 4.2.13.Final (depending on major version line in use)

  1. Identify the current Netty version in use (check pom.xml, build.gradle, or dependency management)
  2. If using Netty 4.1.x line and version is less than 4.1.133.Final, upgrade to 4.1.133.Final
  3. If using Netty 4.2.x line and version is >= 4.2.0 but less than 4.2.13.Final, upgrade to 4.2.13.Final
  4. Update the version in your dependency management file (e.g., pom.xml, build.gradle)
  5. Rebuild the application and run tests to verify compatibility

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
  • Testing6.0 h
  • Review / QA3.0 h
14.0 hours of engineering $2,400
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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-2026-42581 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