Vulnerability · Published Aug 19, 2026 · Assigned by GitHub_M
CVE-2026-75595Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
Critical 9.1
In plain English
A critical-severity security flaw in netty from netty. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | netty | no fix listed | DEBIAN-CVE-2026-75595 |
| Debian:13 | netty | no fix listed | DEBIAN-CVE-2026-75595 |
| Debian:14 | netty | no fix listed | DEBIAN-CVE-2026-75595 |
| Maven | io.netty:netty-handler | 4.2.17.Final | GHSA-c4c3-7fpv-j4q5 |
| Maven | io.netty:netty-handler | 4.1.137.Final | GHSA-c4c3-7fpv-j4q5 |
| Ubuntu:26.10 | netty | no fix listed | UBUNTU-CVE-2026-75595 |
Affected products (as reported)
Weakness: CWE-754 · Vector: 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
References
- https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5 x_refsource_CONFIRM
- https://github.com/netty/netty/pull/17213 x_refsource_MISC
- https://github.com/netty/netty/pull/17217 x_refsource_MISC
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 x_refsource_MISC
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.1.137.Final x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.2.17.Final x_refsource_MISC