CVE-2026-75595Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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
- 9.1 CRITICAL (v4.0, CNA)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
- Weakness (CWE)
- CWE-754
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Aug 20, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
netty netty netty:netty (from the name) | before 4.1.137.Final; from 4.2.0.Final, < 4.2.17.Final | CNA record |
netty netty netty:netty | before 4.1.137; from 4.2.0 before 4.2.17 | NVD |
References
- https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5x-refsource-confirm, vendor-advisory
- https://github.com/netty/netty/pull/17213x-refsource-misc, issue-tracking, patch
- https://github.com/netty/netty/pull/17217x-refsource-misc, issue-tracking, patch
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7x-refsource-misc, patch
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961x-refsource-misc, patch
- https://github.com/netty/netty/releases/tag/netty-4.1.137.Finalx-refsource-misc, release-notes
- https://github.com/netty/netty/releases/tag/netty-4.2.17.Finalx-refsource-misc, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.