`CVE-2026-75596`

8.7 High No exploit published

Published 27 days ago. NVD backfills CPE data for days or weeks after publication, and OSV and the exploit indexes lag too. 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.

CWE-407

Exploitation Status

No public exploit

Nothing published shows this CVE being exploited, which is not the same as ruling it out.

CVSS E:U

CISA KEV not listed
CISA Vulnrichment exploitation: none
Indexed PoC none indexed
EPSS 0.35% chance in 30 days

Waratek Defense Posture

No exploit published

In RASP's scope with an upstream fix path, but nobody has published a working exploit. That is a statement about what has been published, not a finding that the defect is unreachable or unimportant.

Protection none
Action unverified patch rule
Review automated upstream-data
Record active

Decided by no-exploit-published : A published working exploit for this candidate, not only a proof of concept, a forecast, or nothing at all

Finding This CVE is not listed in CISA KEV, CISA Vulnrichment records no active exploitation, and no reviewed exploit catalogue carries an entry for it. Nobody has published something a stranger can run, 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

Decided by	`no-exploit-published` : A published working exploit for this candidate, not only a proof of concept, a forecast, or nothing at all
Finding	This CVE is not listed in CISA KEV, CISA Vulnrichment records no active exploitation, and no reviewed exploit catalogue carries an entry for it. Nobody has published something a stranger can run, 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

1 metric

VRT selects the newest version's highest entry and publishes it as cvssScore, newest rather than largest because scores are not comparable across versions, and highest rather than first because the first entry is frequently a CNA placeholder scoring 0.0 over NVD's own analysis.

Version Score Band Vector Assigner Type

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

Version	Score	Band	Vector	Assigner	Type
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

Affected Software & Releases

☕ Maven Library Packages

Artifact coordinates and fix boundaries from OSV.dev

Package Coordinate Introduced Fixed Last affected

io.netty:netty-handler 4.2.0.Final 4.2.17.Final unbounded

io.netty:netty-handler 0 4.1.137.Final unbounded

Package Coordinate	Introduced	Fixed	Last affected
`io.netty:netty-handler`	4.2.0.Final	`4.2.17.Final`	unbounded
`io.netty:netty-handler`	0	`4.1.137.Final`	unbounded

🖥️ Product CPEs & Version Ranges

1 product(s) over 2 version claims (uncapped)

Source	Vendor	Product	Scheme	Affected Versions
osv	io.netty	netty-handler	generic	＜ 4.1.137 · ≥ 4.2.0 and ＜ 4.2.17

Source

Vendor

Product

Scheme

Affected Versions

osv

io.netty

netty-handler

generic

＜ 4.1.137 · ≥ 4.2.0 and ＜ 4.2.17

References

URL	Tags
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

URL

Timeline

Published 2026-08-19 Last modified 2026-09-09

Published	2026-08-19	By the CVE Program.
NVD record modified	2026-09-09	NVD's own last-modified date for this record.

Published

2026-08-19

By the CVE Program.

NVD record modified

2026-09-09

NVD's own last-modified date for this record.

Pipeline policy audit (15 of 21 rules evaluated)

15 of 21 rules ran. The rest were never reached, because an earlier stage settled the CVE, a distinct claim from a rule that ran and found nothing.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? first match wins

1 rejected no-match CVE Program withdrawal of this identifier

scope: Is the vulnerability ARMR's to address? first match wins

2 armr-patch-file no-match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no-match An ARMR security-rule template on disk for this CVE

4 manual-classification no-match A researcher's recorded decision for this specific CVE

5 manual classification no-match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no-match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no-match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the native WebLogic proxy plug-in. Oracle gives these no CPE of their own and names them only in the description.

8 osv-maven matched Queued for review Maven packages: io.netty:netty-handler

9 cna-maven-package not-reached An affected Maven artifact named by the CNA itself

10 known-cpe-product not-reached An NVD CPE naming a product ARMR tracks

11 cna-cpe-product not-reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

12 oracle-advisory-family not-reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

13 non-deployable-product not-reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

14 unmatched-product not-reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? cumulative: every rule gets a turn

15 patch-hint matched Mitigation candidate References include candidate fix URL (commit tier): https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7

16 open-source-maven skipped The affected package being open source on Maven, so the fix can be read

17 poc-derivable skipped An indexed exploit to reverse-engineer, where there is no source to read

18 no-exploit skipped With no fix path, a public exploit, or a CISA record of one

19 secure-rule-match no-match A vulnerability class already blocked by an ARMR security rule

20 below-action-threshold no-match Severity is HIGH — only MEDIUM/LOW are deprioritized

21 no-exploit-published decided it matched No exploit published No working exploit has been published, and an upstream fix path does exist, so the remediation half of the candidacy still holds.

Raw stored JSON document for this CVE ↗ · NVD ↗ · CVE.org ↗