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

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. Vendors: Maven, Netty, 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
    # 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

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