Answer in brief
CVE-2026-75596 records a Medium severity (CVSS 8.7) vulnerability in Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing. The current sources do not mark it as known exploited. The current feed maps netty/netty (generic), io.netty:netty-handler (maven), io.netty:netty-handler (maven), io.netty:netty-handler (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 8.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps netty/netty (generic), io.netty:netty-handler (maven), io.netty:netty-handler (maven), io.netty:netty-handler (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| netty/nettygeneric | <4.1.137.Final || >=4.2.0.Final <4.2.17.Final | 4.1.137.Final, 4.2.17.Final |
| io.netty:netty-handlermaven | >=0 <4.1.137.Final | 4.1.137.Final |
| io.netty:netty-handlermaven | >=4.2.0.Final,<=4.2.16.Final | 4.2.17.Final |
| io.netty:netty-handlermaven | <=4.1.136.Final | 4.1.137.Final |
| io.netty:netty-handlermaven | >=4.2.0.Final <4.2.17.Final | 4.2.17.Final |
Published upstream
Aug 19, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 19, 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.
Quoted source text, attributed separately from HOL analysis.