---
id: CVE-2026-63983
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: fix packet loop on netem when duplicate is on

  When netem duplicates a packet it re-enqueues the copy at the root qdisc.
  If another netem sits in the tree th…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: fix packet loop on netem when duplicate is on

  When netem duplicates a packet it re-enqueues the copy at the root qdisc.
  If another netem sits in the tree th…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 0afb51e72855971dba83b3c6b70c547c2d1161fd <
    1a298a514ce766c6d0c232991a390fec67af81ad
  - >-
    Linux >= 0afb51e72855971dba83b3c6b70c547c2d1161fd <
    4ec3a8ca97394f17e73a4d8d4c79c1c78b322772
  - >-
    Linux >= 0afb51e72855971dba83b3c6b70c547c2d1161fd <
    cfb2616042767ab31260d4f39190c381bec8b12e
  - >-
    Linux >= 0afb51e72855971dba83b3c6b70c547c2d1161fd <
    9552b11e3edabc97cfcd9f29103d5afbce7ae183
  - Linux 2.6.12
published: '2026-07-19'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T11:17:38.033'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63983'
references:
  - url: 'https://git.kernel.org/stable/c/1a298a514ce766c6d0c232991a390fec67af81ad'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4ec3a8ca97394f17e73a4d8d4c79c1c78b322772'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9552b11e3edabc97cfcd9f29103d5afbce7ae183'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cfb2616042767ab31260d4f39190c381bec8b12e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
epss: 0.00206
epssPercentile: 0.0996
ingestedAt: '2026-10-15T11:00:41.697Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

net/sched: fix packet loop on netem when duplicate is on

When netem duplicates a packet it re-enqueues the copy at the root qdisc.
If another netem sits in the tree the copy can be duplicated
again, recursing until the stack or memory is exhausted.

The original duplication guard temporarily zeroed q->duplicate around
the re-enqueue, but that does not cover all cases because it is
per-qdisc state shared across all concurrent enqueue paths
and is not safe without additional locking.

Use the skb tc_depth field introduced in an earlier patch:
 - increment it on the duplicate before re-enqueue
 - skip duplication for any skb whose tc_depth is already non-zero.

This marks the packet itself rather than mutating qdisc state,
therefore it is safe regardless of tree topology or concurrency.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.