CVE-2026-75596
Published:August 19, 2026
Updated:September 24, 2026
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 Packages
https://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.2.0.Final <netty-4.2.17.FinalFix Suggestion:
Update to version netty-4.2.17.Finalhttps://github.com/netty/netty.git (GITHUB):
Affected version(s) >=netty-4.1.0.Final <netty-4.1.137.FinalFix Suggestion:
Update to version netty-4.1.137.Finalio.netty:netty-handler (JAVA):
Affected version(s) >=4.0.0.Alpha1 <4.1.137.FinalFix Suggestion:
Update to version 4.1.137.Finalio.netty:netty-handler (JAVA):
Affected version(s) >=4.2.0.Final <4.2.17.FinalFix Suggestion:
Update to version 4.2.17.Finalio.netty:netty-handler (JAVA):
Affected version(s) >=4.0.0.Alpha1 <4.1.137.FinalFix Suggestion:
Update to version 4.1.137.FinalRelated Resources (10)
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Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Inefficient Algorithmic Complexity
EPSS
Base Score:
0.39