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CVE-2026-75596

CVE-2026-75596 · Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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 8.7 · High · EPSS 0.4%

Published
Updated

Stack: system

Affected products and versions

  • netty

    Versions
    • < 4.1.137.Final: Affected
    • >= 4.2.0.Final, < 4.2.17.Final: Affected

    No fix published

  • netty Debian:12

    Versions
    • 1:4.1.48-10
    • 1:4.1.48-11
    • 1:4.1.48-12
    • 1:4.1.48-13
    • 1:4.1.48-14
    • 1:4.1.48-15
    • 1:4.1.48-16
    • 1:4.1.48-7
    • 1:4.1.48-7+deb12u1
    • 1:4.1.48-7+deb12u2
    • 1:4.1.48-8
    • 1:4.1.48-9
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Debian:13

    Versions
    • 1:4.1.48-10
    • 1:4.1.48-10+deb13u1
    • 1:4.1.48-11
    • 1:4.1.48-12
    • 1:4.1.48-13
    • 1:4.1.48-14
    • 1:4.1.48-15
    • 1:4.1.48-16
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Debian:14

    Versions
    • 1:4.1.48-10
    • 1:4.1.48-11
    • 1:4.1.48-12
    • 1:4.1.48-13
    • 1:4.1.48-14
    • 1:4.1.48-15
    • 1:4.1.48-16
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:14.04:LTS

    Versions
    • 1:3.2.6.Final-2
    • 1:3.2.6.Final-2+deb8u2build0.14.04.1~esm1
    • 1:3.2.6.Final-2+deb8u2ubuntu0.1~esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:16.04:LTS

    Versions
    • 1:3.2.6.Final-2
    • 1:4.0.32-1
    • 1:4.0.33-1
    • 1:4.0.34-1
    • 1:4.0.34-1ubuntu0.1~esm1
    • 1:4.0.34-1ubuntu0.1~esm2
    • 1:4.0.34-1ubuntu0.1~esm3
    • 1:4.0.34-1ubuntu0.1~esm4
    • 1:4.0.34-1ubuntu0.1~esm5
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:18.04:LTS

    Versions
    • 1:4.1.7-4
    • 1:4.1.7-4ubuntu0.1~esm1
    • 1:4.1.7-4ubuntu0.1
    • 1:4.1.7-4ubuntu0.1+esm1
    • 1:4.1.7-4ubuntu0.1+esm2
    • 1:4.1.7-4ubuntu0.1+esm3
    • 1:4.1.7-4ubuntu0.1+esm4
    • 1:4.1.7-4ubuntu0.1+esm5
    • 1:4.1.7-4ubuntu0.1+esm6
    • 1:4.1.7-4ubuntu0.1+esm7
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:20.04:LTS

    Versions
    • 1:4.1.33-1
    • 1:4.1.33-2
    • 1:4.1.33-3
    • 1:4.1.45-1
    • 1:4.1.45-1ubuntu0.1~esm1
    • 1:4.1.45-1ubuntu0.1~esm2
    • 1:4.1.45-1ubuntu0.1~esm3
    • 1:4.1.45-1ubuntu0.1~esm4
    • 1:4.1.45-1ubuntu0.1~esm6
    • 1:4.1.45-1ubuntu0.1~esm7
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:22.04:LTS

    Versions
    • 1:4.1.48-4
    • 1:4.1.48-4+deb11u1build0.22.04.1
    • 1:4.1.48-4+deb11u2build0.22.04.1
    • 1:4.1.48-4+deb11u2ubuntu0.1~esm1
    • 1:4.1.48-4+deb11u2ubuntu0.1~esm2
    • 1:4.1.48-4+deb11u2ubuntu0.1
    • 1:4.1.48-4+deb11u2ubuntu0.1+esm1
    • 1:4.1.48-4+deb11u2ubuntu0.1+esm3
    • 1:4.1.48-4+deb11u2ubuntu0.2
    • 1:4.1.48-4+deb11u2ubuntu0.2+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:24.04:LTS

    Versions
    • 1:4.1.48-7
    • 1:4.1.48-8
    • 1:4.1.48-9
    • 1:4.1.48-9ubuntu0.1~esm1
    • 1:4.1.48-9ubuntu0.1~esm2
    • 1:4.1.48-9ubuntu0.1
    • 1:4.1.48-9ubuntu0.1+esm1
    • 1:4.1.48-9ubuntu0.1+esm3
    • 1:4.1.48-9ubuntu0.2
    • 1:4.1.48-9ubuntu0.2+esm1
    • 1:4.1.48-9ubuntu0.2+esm2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:26.10

    Versions
    • 1:4.1.48-16
    • 1:4.1.48-16ubuntu1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • netty Ubuntu:Pro:26.04:LTS

    Versions
    • 1:4.1.48-10
    • 1:4.1.48-11
    • 1:4.1.48-12
    • 1:4.1.48-13
    • 1:4.1.48-14
    • 1:4.1.48-16
    • 1:4.1.48-16ubuntu0.1~esm2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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