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Vulnerability record · CVE-2026-75595 · published 19 August 2026

CVE-2026-75595: Netty vulnerability

Netty · Netty

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.

9.1 CVSS 4.0 Critical EPSS 0.46% · top 62.9% CWE-754 · CWE-754
9.1CVSS 4.0 base score
0.46%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
7References
22 Sep 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 Patch
https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 Patch
https://github.com/netty/netty/pull/17213 Issue TrackingPatch
https://github.com/netty/netty/pull/17217 Issue TrackingPatch
https://github.com/netty/netty/releases/tag/netty-4.1.137.Final Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.17.Final Release Notes
https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5 Vendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-75595), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.