# CVE-2026-75595: Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext

> CVE-2026-75595: Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext. CVSS 9.1 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-75595
Last updated: 2026-09-22T19:33:26Z

- Published: 2026-08-19 21:00 UTC · Updated: 2026-09-22 19:33 UTC · Assigner: GitHub\_M
- CVSS: 9.1 (CVSS 3.1) · Severity: Critical · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- EPSS: 0.32%, 24th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-754

## 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 vendors and products

- netty: netty

## Tracked companies

- [Confluence](https://rewindex.com/company/confluence.md)
- [Jira](https://rewindex.com/company/jira.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-75595)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-75595)
- [https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7](https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7)
- [https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961](https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961)
- [https://github.com/netty/netty/pull/17213](https://github.com/netty/netty/pull/17213)
- [https://github.com/netty/netty/pull/17217](https://github.com/netty/netty/pull/17217)
- [https://github.com/netty/netty/releases/tag/netty-4.1.137.Final](https://github.com/netty/netty/releases/tag/netty-4.1.137.Final)
- [https://github.com/netty/netty/releases/tag/netty-4.2.17.Final](https://github.com/netty/netty/releases/tag/netty-4.2.17.Final)
- [https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5](https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-75595 · Markdown: https://rewindex.com/cve/CVE-2026-75595.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-75595 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:09:53.236Z