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

Quick assessment

Affected
netty netty
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Netty是Netty团队开源的一个高性能网络通信框架。 Netty 4.1.137.Final之前版本和4.2.17.Final之前版本存在资源管理错误漏洞，该漏洞源于SniHandler在预握手ClientHello聚合路径中对每个额外的TLS记录重新复制所有先前收到的正文字节，导致CPU工作量呈二次方增长，未经身份验证的远程攻击者可利用大型ClientHello和数千个微小记录降低TLS处理性能，造成拒绝服务。

CVSS 8.7 · High EPSS 0.35% · P28

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
netty netty < 4.1.137.Final affected
>= 4.2.0.Final, < 4.2.17.Final affected
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I. Basic Information for CVE-2026-75596

Vulnerability Information
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Vulnerability Title
Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
Netty 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Netty是Netty团队开源的一个高性能网络通信框架。 Netty 4.1.137.Final之前版本和4.2.17.Final之前版本存在资源管理错误漏洞，该漏洞源于SniHandler在预握手ClientHello聚合路径中对每个额外的TLS记录重新复制所有先前收到的正文字节，导致CPU工作量呈二次方增长，未经身份验证的远程攻击者可利用大型ClientHello和数千个微小记录降低TLS处理性能，造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
netty netty < 4.1.137.Final -

II. Public POCs for CVE-2026-75596

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 14539 chars
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III. Intelligence Information for CVE-2026-75596

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Patches & Fixes for CVE-2026-75596 (2)

Vendor Advisories for CVE-2026-75596 (1)

Vendor Pages for CVE-2026-75596 (1)

IV. Related Vulnerabilities

Same product: netty
Same vendor: netty
Same weakness: CWE-407

V. Comments for CVE-2026-75596

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