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🛡️ CVE-2026-42577 — netty

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-772 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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](https://github.com/netty/netty/pull/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 ALLOW_HALF_CLOSURE 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 SO_LINGER=0)

the server-side channel is never closed. This happens because:

  • epollOutReady() is a no-op when there is no pending flush.
  • epollInReady() short-circuits via shouldBreakEpollInReady() because input is already marked as shutdown.
  • The EPOLLERR/EPOLLHUP error condition is therefore never processed, and channelInactive is never fired.

Depending on the Netty version and configuration, this results in:

  • Stale channels: The connection is never closed or deregistered. An unauthenticated remote attacker can repeat the sequence to accumulate stale connections, exhausting file descriptors, memory, or connection-count limits.
  • CPU busy-loop: In code paths where clearEpollIn0() is not called during the ChannelInputShutdownReadComplete event, epoll_wait returns immediately on every iteration for the affected fd, causing 100% CPU utilization on the event loop thread and starving all other connections multiplexed on it.

Mitigation

  • Upgrade to 4.2.13.Final when released (or build from the 4.2 branch at commit [0ec3d97](https://github.com/netty/netty/commit/0ec3d97fab376e243d328ac95fbd288ba0f6e22d)).
  • If upgrading is not immediately possible, configure idle timeouts on connections to limit the lifetime of stale channels.

References

  • Issue: https://github.com/netty/netty/issues/16683
  • Fix: https://github.com/netty/netty/pull/16689

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-42577 is classified as CWE-772: Missing Release of Resource. A resource is acquired but never released on some paths, depleting the pool over time.

Affected software

CVE-2026-42577 is recorded against 2 packages.

  • io.netty:netty-transport-classes-epoll (from 4.2.0.Final up to 4.2.13.Final)
  • netty (from 4.2.0 up to 4.2.13)

Timeline and source

Published on 6 May 2026 and last revised on 24 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
github.com (Package)

Other advisories for this package

io.netty:netty-transport-classes-epoll has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-772: Missing Release of Resource) in other software:

CVE-2026-42577 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-772
Public Exploit ✅ No
Source NVD
Published 2026-05-06
Updated 2026-08-20
Modified 2026-07-24

Affected Packages

Software From version Fixed in
io.netty:netty-transport-classes-epoll 4.2.0.Final 4.2.13.Final
netty 4.2.0 4.2.13

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