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.
Affected products
netty: netty
References7
- github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 Vendor Advisory
- github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7d… Patch
- github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139… Patch
- github.com/netty/netty/pull/17213 Issue TrackingPatch
- github.com/netty/netty/pull/17217 Issue TrackingPatch
- github.com/netty/netty/releases/tag/netty-4.1.137.Final Release Notes
- github.com/netty/netty/releases/tag/netty-4.2.17.Final Release Notes
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 4.0
-
8.7
HIGH
Score source: CNA
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 — exploit probability
- 0% percentile: 32 · as of 10 November 2026
- CWE
- CWE-407
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