Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-75596
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-19 21:17:37 UTC
Updated2026-08-20 20:17:46 UTC
DescriptionNetty 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.

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from [email protected]

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

EPSS: 0.003500000 probability, percentile 0.282630000 (date 2026-08-20)

Problem Types: CWE-407 | CWE-407 CWE-407: Inefficient Algorithmic Complexity

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary8.7HIGHCVSS: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/C...
4.0CNADECLARED8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Netty Netty affected < 4.1.137.Final Not specified
CNA Netty Netty affected >= 4.2.0.Final, < 4.2.17.Final Not specified

References

ReferenceSourceLinkTags
github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 [email protected] github.com
github.com/netty/netty/releases/tag/netty-4.1.137.Final [email protected] github.com
github.com/netty/netty/pull/17217 [email protected] github.com
github.com/netty/netty/pull/17213 [email protected] github.com
github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 [email protected] github.com
github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 [email protected] github.com
github.com/netty/netty/releases/tag/netty-4.2.17.Final [email protected] github.com
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