Answer in brief
CVE-2026-75595 records a Critical severity (CVSS 9.1) vulnerability in Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext. 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 9.1. 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 | >=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 |
| io.netty:netty-handlermaven | >=0 <4.1.137.Final | 4.1.137.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.Fina and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
Quoted source text, attributed separately from HOL analysis.