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

Source: https://junglewise.ai/threats/cve-2026-42577-netty-denial-of-service-in-epoll-transport-via-rst-on-half-closed  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-42577 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty, a widely used networking framework for Java applications, contains a flaw in its Linux-specific networking component. An attacker can send specially timed network signals to cause the server to stop cleaning up old connections or enter a state of 100% CPU usage. This can lead to a complete service outage by exhausting system resources or making the server unresponsive to legitimate users.

Technologies: [Netty](https://junglewise.ai/threats/technologies/netty). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty](https://junglewise.ai/threats/vendors/netty), [Netty Project](https://junglewise.ai/threats/vendors/netty-project).

## Quick answers

**Is CVE-2026-42577 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42577 being exploited in the wild.

**How severe is CVE-2026-42577?** High severity, with a CVSS score of 7.5, published 13 May 2026.

**Which products and versions are affected?** io.netty:netty-transport-classes-epoll (Maven) >= 4.2.0.Final, < 4.2.13.Final, ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.13.Final; io.netty:netty-transport-native-epoll (Maven) >= 4.2.0.Final, < 4.2.13.Final; Netty Project Transport Classes Epoll >= 4.2.0.Final, < 4.2.13.Final.

**Is there a fix for CVE-2026-42577?** Yes. io.netty:netty-transport-classes-epoll (Maven): upgrade to 4.2.13.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42577 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42577?** Check whether you run io.netty:netty-transport-classes-epoll (Maven), io.netty:netty-transport-native-epoll (Maven), Netty or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-transport-classes-epoll (Maven): upgrade to 4.2.13.Final or later

  ```sh
  # set io.netty:netty-transport-classes-epoll to 4.2.13.Final in your pom.xml or build.gradle
  ```


## Technical details

A vulnerability exists in Netty's epoll transport when ALLOW_HALF_CLOSURE is enabled or when using the HTTP codec. If a remote peer sends a FIN followed by a RST (e.g., via SO_LINGER=0), the server-side channel fails to close because epollInReady() short-circuits and the EPOLLERR/EPOLLHUP conditions are never processed. This leads to resource exhaustion via stale file descriptors or a CPU busy-loop if clearEpollIn0() is not called, starving other multiplexed connections. The issue is fixed in version 4.2.13.Final by ensuring proper error condition processing during half-closure states.

## Affected products

- Netty netty-transport-classes-epoll >= 4.2.0.Final, < 4.2.13.Final

## Identifiers

- CVE-2026-42577
- GHSA-rwm7-x88c-3g2p

## Timeline

- 2026-04-25: other: Fix merged into 4.2 branch
- 2026-05-05: disclosed
- 2026-05-06: advisory

## References

- [https://api.github.com/users/Stormpx](https://api.github.com/users/Stormpx)
- [https://github.com/Stormpx](https://github.com/Stormpx)
- [https://api.github.com/users/Stormpx/gists%7B/gist_id%7D](https://api.github.com/users/Stormpx/gists%7B/gist_id%7D)
- [https://api.github.com/users/Stormpx/repos](https://api.github.com/users/Stormpx/repos)
- [https://avatars.githubusercontent.com/u/31039456?v=4](https://avatars.githubusercontent.com/u/31039456?v=4)
- [https://api.github.com/users/Stormpx/events%7B/privacy%7D](https://api.github.com/users/Stormpx/events%7B/privacy%7D)

## Related threats

- [Netty HTTP/1 decoder request smuggling](https://junglewise.ai/threats/cve-2026-93562-a-flaw-was-found-in-netty-s-http-1-decoder-incomplete-validation)
- [Netty HTTP/1 to HTTP/2 conversion authority mismatch](https://junglewise.ai/threats/cve-2026-93569-netty-http-1-to-http-2-conversion-authority-mismatch)
- [Netty HTTP request smuggling via control characters in chunk size](https://junglewise.ai/threats/cve-2026-93566-netty-http-request-smuggling-via-control-characters-in-chunk-size)
- [Netty RtspDecoder method-token smuggling in RTSP parsing](https://junglewise.ai/threats/cve-2026-93565-netty-rtspdecoder-method-token-smuggling-in-rtsp-parsing)
- [Netty reference-count leak in HAProxy PROXY-v2 decoder](https://junglewise.ai/threats/cve-2026-93564-netty-reference-count-leak-in-haproxy-proxy-v2-decoder)