CVE-2026-75596

UNKNOWN 0.0

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

CVSS Score

0.0

EPSS Score

0.0%

EPSS Percentile

0th

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	CWE-407
Vendor	netty
Product	netty
Published	Aug 19, 2026

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Affected Versions

netty / netty

< 4.1.137.Final >= 4.2.0.Final, < 4.2.17.Final

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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