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Vulnerability record · CVE-2026-75596 · published 19 August 2026

CVE-2026-75596: Netty vulnerability

Netty · Netty

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.

8.7 CVSS 4.0 High EPSS 0.69% · top 49.2% CWE-407 · CWE-407
8.7CVSS 4.0 base score
0.69%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
7References
22 Sep 2026Last modified by NVD

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.

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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 Patch
https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 Patch
https://github.com/netty/netty/pull/17213 Issue TrackingPatch
https://github.com/netty/netty/pull/17217 Issue TrackingPatch
https://github.com/netty/netty/releases/tag/netty-4.1.137.Final Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.17.Final Release Notes
https://github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-75596), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.