Netty epoll transport denial of service via RST on half-closed TCP connection

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-42577: 0.41% estimated exploitation activity in the next 30 days; percentile 35.12 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Affected versions All versions of 4.2.x netty-transport-classes-epoll up to and including 4.2.12.Final Fixed in 4.2.13.Final (fix merged into the 4.2 branch via #16689; release not yet cut as of 2026-04-25). Severity Medium — Denial of Service (resource exhaustion / CPU spin) CVSS: 3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - 7.5 CWE: CWE-772: Missing Release of Resource after Effective Lifetime Description When a TCP connection using Netty's epoll transport has ALLOWHALFCLOSURE enabled (or is in a half-closed state via the HTTP codec), and the remote peer: 1. Sends a FIN (half-close), causing the server to mark the input as shutdown, then 2. Sends a RST (e.g. by closing with SOLINGER=0) the server-side channel is never closed. This happens because:…

Published by the source

6 May 2026, 23:10 UTC

Last modified by the source

24 Jul 2026, 19:05 UTC

Source last checked

26 Oct 2026, 16:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-rwm7-x88c-3g2p

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# Patch Next advisory brief: CVE-2026-42577

Advisory: Netty epoll transport denial of service via RST on half-closed TCP connection
IDs: CVE-2026-42577, GHSA-rwm7-x88c-3g2p
Record: https://patchnext.com/advisories/cve-2026-42577 (revision 1, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-transport-classes-epoll 4.2.13.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-transport-classes-epoll: affected >= 4.2.0.Final, < 4.2.13.Final; fixed in 4.2.13.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-transport-classes-epoll: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-transport-classes-epoll.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-rwm7-x88c-3g2p (GitHub-reviewed advisory GHSA-rwm7-x88c-3g2p lists affected ranges: Maven io.netty:netty-transport-classes-epoll >=4.2.0.Final <4.2.13.Final)

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