WaratekVRT Sign in

CVE-2026-75596 Netty

Affected softwareNetty
Severity8.7 High CVSS 4.0 2 scores
Fixed in4.2.17.Final, 4.1.137.Final
WeaknessCWE-407
Published19 Aug 2026
Updated26 Oct 2026

Published 2 months ago. NVD often adds the list of affected products days or weeks after a CVE is published, and the other sources we check lag too. The scope and status here may change.

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Exploitation status

No public exploit

No exploit has been reported in the sources we check.

  • CISA KEV not listed
  • VulnCheck KEV not listed
  • CISA Vulnrichment exploitation: none
  • Indexed PoC none indexed
  • EPSS 0.37% chance in 30 days

Waratek protection

No exploit published

Within Waratek scope. In the sources we check, nobody has published exploit code for this CVE or reported it being exploited.

A public code fix exists: netty/netty 1b5abc6.

  • Protection none
  • Action unverified
  • Review automated Upstream data
  • Record active
Decided by Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all
Finding This CVE is not listed in CISA KEV or VulnCheck KEV, CISA Vulnrichment records no active exploitation, no reviewed exploit catalogue carries an entry for it, and no GitHub PoC repository for it has 5 or more stars. Nobody has published exploit code worth tracing, so it is not a candidate for a rule ahead of the ones where somebody has; an upstream fix path does exist, so the remediation half of the candidacy still holds. This is a statement about what has been published, not about whether the defect is reachable or serious.
Candidate fix https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 : a commit: the change itself

CVSS

8.7 HIGH v4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

VersionScoreBandVectorAssignerType
CVSS 4.0 8.7 HIGH CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X security-advisories@github.com Secondary published
CVSS 3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H NVD Primary

Affected software and releases

Oracle advisories

AdvisoryTypeQuarterProducts Oracle names in its risk matrix
Oracle Critical Patch Update October 2026 ↗ CPU 2026-Q4 Oracle Communications / Core (Netty) (6.1.1-7.0.0)

Oracle components and versions

FamilyComponentVersions, as Oracle lists themRead as
Oracle Communications Core (Netty) 6.1.1-7.0.0

Maven packages

Affected and fixed versions, from OSV.dev
PackageIntroducedFixedLast affected
io.netty:netty-handler 4.2.0.Final 4.2.17.Final unbounded
io.netty:netty-handler 0 4.1.137.Final unbounded

Products and versions

2 products, 4 version entries
SourceVendorProductSchemeAffected versions
osv io.netty netty-handler generic < 4.1.137 · ≥ 4.2.0 and < 4.2.17
nvd netty netty generic < 4.1.137 · ≥ 4.2.0 and < 4.2.17

References

URLTags
https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 commit
https://github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 WEB
https://github.com/netty/netty/pull/17213 WEB
https://github.com/netty/netty/pull/17217 WEB
https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 WEB
https://github.com/netty/netty PACKAGE
https://github.com/netty/netty/releases/tag/netty-4.1.137.Final WEB
https://github.com/netty/netty/releases/tag/netty-4.2.17.Final WEB

Timeline

Published2026-08-19By the CVE Program.
NVD record modified2026-10-26NVD's own last-modified date for this record.