CVE-2026-75595: Netty

Critical severity, CVSS 9.1. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Netty Netty: before 4.1.137 (fixed in 4.1.137); from 4.2.0, before 4.2.17 (fixed in 4.2.17)

Published 2026-08-19. Last modified 2026-09-22.