# CVE-2026-75595

## Summary

- **CVE ID:** CVE-2026-75595
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-754
- **Published:** Aug 19, 2026
- **Last Modified:** Aug 20, 2026

## Description

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 (< 4.1.137.Final)
- netty — netty (>= 4.2.0.Final, < 4.2.17.Final)

## References

- [CNA](https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5)
- [CNA](https://github.com/netty/netty/pull/17213)
- [CNA](https://github.com/netty/netty/pull/17217)
- [CNA](https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7)
- [CNA](https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961)
- [CNA](https://github.com/netty/netty/releases/tag/netty-4.1.137.Final)
- [CNA](https://github.com/netty/netty/releases/tag/netty-4.2.17.Final)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.32%
- **EPSS Percentile:** 24.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._