CVE-2026-75596High· 7.5▾ TwilightNetty 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/mai…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.4%
Last analysed / modified upstream
— → 7.5
medium → high
0.4% → 0.7%
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.
netty < 4.1.137netty >= 4.2.0, < 4.2.17Upgrade past the affected range:
netty 4.2.17Affected packages:
io.netty:netty-handler >= 4.2.0.Final, <= 4.2.16.Finalio.netty:netty-handler <= 4.1.136.FinalPatched in:
io.netty:netty-handler 4.2.17.Finalio.netty:netty-handler 4.1.137.FinalField changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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