Vulnerability Details CVE-2026-75595
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 24.9%
CVSS Severity
CVSS v3 Score 9.1
References
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961
- https://github.com/netty/netty/pull/17213
- 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-4.2.17.Final
- https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5
Products affected by CVE-2026-75595
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cpe:2.3:a:netty:netty:4.2.0
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cpe:2.3:a:netty:netty:4.2.1
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cpe:2.3:a:netty:netty:4.2.10
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cpe:2.3:a:netty:netty:4.2.11
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cpe:2.3:a:netty:netty:4.2.12
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cpe:2.3:a:netty:netty:4.2.13
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cpe:2.3:a:netty:netty:4.2.14
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cpe:2.3:a:netty:netty:4.2.15
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cpe:2.3:a:netty:netty:4.2.16
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cpe:2.3:a:netty:netty:4.2.2
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cpe:2.3:a:netty:netty:4.2.3
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cpe:2.3:a:netty:netty:4.2.4
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cpe:2.3:a:netty:netty:4.2.5
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cpe:2.3:a:netty:netty:4.2.6
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cpe:2.3:a:netty:netty:4.2.7
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cpe:2.3:a:netty:netty:4.2.8
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cpe:2.3:a:netty:netty:4.2.9