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NettyApplication

CVE-2026-55831

HIGH · 7.5 CVSS v3.1 Developing Published 2026-07-21
Fix available
A fix is available. Upgrade to 4.1.136 / 4.2.16 or later.
See remediation →
84/100
Remediation priority · High
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. Prior to 4.1.136.Final and 4.2.16.Final, Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in `DefaultSpdySettingsFrame`, allowing a remote SPDY/3.1 peer to send a syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries and amplifies network input into heap growth and ordered-map insertion work. 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 · low confidence
Developing — this CVE was published recently and its authoritative NVD entry is still being established, so we're holding a technical summary until the source data settles rather than publish something unreliable. Re-checking after 2026-08-04.

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
None
Integrity
None
Availability
High

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

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
Recommended fix High confidence

Netty 4.1.x -> 4.1.136.Final (or later); Netty 4.2.x -> 4.2.16.Final (or later)

  1. 1. Identify the current Netty version in use by examining project dependencies (e.g., pom.xml, build.gradle, or similar dependency management files)
  2. 2. Determine which Netty 4.x branch is in use (4.1.x or 4.2.x)
  3. 3. For projects using Netty 4.1.x: upgrade netty-all or io.netty dependencies to version 4.1.136.Final or later
  4. 4. For projects using Netty 4.2.x: upgrade netty-all or io.netty dependencies to version 4.2.16.Final or later
  5. 5. Rebuild and test the application to verify the upgrade does not introduce regressions
  6. 6. Redeploy the updated application
Caveat Review Netty 4.1.136.Final and 4.2.16.Final release notes for any breaking changes between your current version and the fixed version

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

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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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-2026-55831 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
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