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NettyApplication

CVE-2026-50020

MEDIUM · 5.3 CVSS v3.1 Published 2026-06-12
Fix available
A fix is available. Upgrade to 4.1.135 / 4.2.15 or later.
See remediation →
62/100
Remediation priority · Elevated
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 a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, before reading the first request-line, `HttpObjectDecoder` skips every byte for which `Character.isISOControl(b)` is `true` (0x00–0x1F and 0x7F) as well as all whitespace. RFC 9112 §2.2 only asks servers to ignore empty CRLF lines preceding the request-line — a carefully scoped robustness allowance intended to handle HTTP/1.0 POST workarounds. Silently absorbing NUL bytes, SOH, STX, and other non-CRLF control characters goes significantly beyond this, and can be exploited for request-boundary confusion in pipelined or multiplexed transports where a front-end component treats those bytes differently. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

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

The HttpObjectDecoder in Netty improperly skips all ISO control characters (0x00-0x1F and 0x7F) and whitespace before parsing the HTTP request-line, exceeding RFC 9112's allowance of only empty CRLF lines. This behavior can be exploited to cause request-boundary confusion in pipelined or multiplexed HTTP transports where front-end components interpret these control characters differently.

MitigationUpgrade Netty to version 4.1.135.Final, 4.2.15.Final, or later to patch the overly permissive control character handling in HttpObjectDecoder.

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:< 4.1.135>= 4.2.0, < 4.2.15

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
Low
Availability
None

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

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 JAR files in your classpath
    Search for netty-*.jar files in your application lib directories, container lib folder, or examine Maven/Gradle dependencies for 'io.netty' groupId artifacts
    Affected if Netty JARs are present in the runtime classpath
  2. Determine the exact Netty version
    For Maven projects, run 'mvn dependency:tree | grep netty' or inspect the MANIFEST.MF inside the netty-common or netty-codec JAR files. For Gradle, run 'gradle dependencies' and locate netty modules
    Affected if Version is less than 4.1.135 or greater than or equal to 4.2.0 but less than 4.2.15
  3. Confirm netty-codec-http module is in use
    Look for netty-codec-http in your dependency tree, as HttpObjectDecoder resides in this module. Check if your application configures HttpServerCodec, HttpClientCodec, or any HttpMessageDecoder implementation
    Affected if netty-codec-http is loaded and handles HTTP traffic
  4. Check if HTTP pipelining or multiplexing is enabled
    Inspect your server configuration for HTTP/2 (Http2FrameCodec) or HTTP pipelining settings. Look for pipeline configurations that chain multiple requests on a single connection
    Affected if HTTP/2 multiplexing or HTTP pipelining is configured on Netty-based HTTP servers

You are affected if Netty version is below 4.1.135 or between 4.2.0 and 4.2.14 inclusive, AND your application uses netty-codec-http to handle pipelined or multiplexed HTTP connections.

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 4.1.135 / 4.2.15 or later
Fixed in 4.1.1354.2.15
Interim mitigation

Upgrade Netty to version 4.1.135.Final, 4.2.15.Final, or later to patch the overly permissive control character handling in HttpObjectDecoder.

Recommended fix High confidence

4.1.135.Final (for 4.1.x line) or 4.2.15.Final (for 4.2.x line)

  1. 1. Determine your current Netty version by checking your dependency management (Maven pom.xml, Gradle build.gradle, or similar)
  2. 2. Identify which Netty major version line you are using (4.1.x or 4.2.x)
  3. 3. For 4.1.x line: upgrade to version 4.1.135.Final or later
  4. 4. For 4.2.x line: upgrade to version 4.2.15.Final or later
  5. 5. Update your dependency configuration file with the new version
  6. 6. Rebuild and test your application to ensure compatibility
Caveat Minimal risk; this is a security bug fix that changes decoder behavior to be more RFC-compliant by not silently skipping non-CRLF control characters

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

Fix this in Netty Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing8.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,140
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,424.

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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-2026-50020 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