CVE-2026-75595
Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 4.0 | Critical9.1 | 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 |
| NVDNVD · Analyzed | 4.0 | Critical9.1 | 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/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:X/V:X/RE:X/U:X |
- EPSS (exploitation in 30 days)
- 0.32% · top 75% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.1.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Mavenio.netty:netty-handlerGHSA-c4c3-7fpv-j4q5 (opens in a new tab)
References (7)
- https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5 (opens in a new tab)x_refsource_CONFIRM
- https://github.com/netty/netty/pull/17213 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/pull/17217 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.1.137.Final (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.2.17.Final (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-c4c3-7fpv-j4q5 (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-75595)Record last updated .