GHSA-RWM7-X88C-3G2P

Vulnerability from github – Published: 2026-05-06 23:10 – Updated: 2026-07-24 19:05
VLAI
Summary
Netty epoll transport denial of service via RST on half-closed TCP connection
Details

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 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).
  • 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
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-transport-classes-epoll"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.2.0.Final"
            },
            {
              "fixed": "4.2.13.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42577"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-772"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-06T23:10:41Z",
    "nvd_published_at": "2026-05-13T19:17:23Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nNetty\u0027s 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.\n\n## Affected versions\n\nAll versions of 4.2.x `netty-transport-classes-epoll` up to and including 4.2.12.Final\n\n## Fixed in\n\n4.2.13.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).\n\n## Severity\n\n**Medium** \u2014 Denial of Service (resource exhaustion / CPU spin)\n\n**CVSS:** 3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - **7.5**\n\n**CWE:** CWE-772: Missing Release of Resource after Effective Lifetime\n\n## Description\n\nWhen a TCP connection using Netty\u0027s epoll transport has `ALLOW_HALF_CLOSURE` enabled (or is in a half-closed state via the HTTP codec), and the remote peer:\n\n1. Sends a FIN (half-close), causing the server to mark the input as shutdown, then\n2. Sends a RST (e.g. by closing with `SO_LINGER=0`)\n\nthe server-side channel is never closed. This happens because:\n\n- `epollOutReady()` is a no-op when there is no pending flush.\n- `epollInReady()` short-circuits via `shouldBreakEpollInReady()` because input is already marked as shutdown.\n- The `EPOLLERR`/`EPOLLHUP` error condition is therefore never processed, and `channelInactive` is never fired.\n\nDepending on the Netty version and configuration, this results in:\n\n- **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.\n- **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.\n\n## Mitigation\n\n- 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)).\n- If upgrading is not immediately possible, configure idle timeouts on connections to limit the lifetime of stale channels.\n\n## References\n\n- Issue: https://github.com/netty/netty/issues/16683\n- Fix: https://github.com/netty/netty/pull/16689",
  "id": "GHSA-rwm7-x88c-3g2p",
  "modified": "2026-07-24T19:05:52Z",
  "published": "2026-05-06T23:10:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/security/advisories/GHSA-rwm7-x88c-3g2p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42577"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/pull/16689"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/commit/0ec3d97fab376e243d328ac95fbd288ba0f6e22d"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/netty/netty"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Netty epoll transport denial of service via RST on half-closed TCP connection"
}



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