---
id: CVE-2021-47014
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: act_ct: fix wild memory access when clearing fragments

  while testing re-assembly/re-fragmentation using act_ct, it's possible to
  observe a crash like the fo…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: act_ct: fix wild memory access when clearing fragments

  while testing re-assembly/re-fragmentation using act_ct, it's possible to
  observe a crash like the fo…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-754
  - CWE-119
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.8, < 5.12.4'
patched:
  - linux_kernel 5.12.4
published: '2024-02-28'
updated: '2026-08-04'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-47014'
references:
  - url: 'https://git.kernel.org/stable/c/0648941f4c8bbf8b4b6c0b270889ae7aa769b921'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/0648941f4c8bbf8b4b6c0b270889ae7aa769b921'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47014.json
  - url: 'https://access.redhat.com/security/cve/CVE-2021-47014'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2266738'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2021-47014'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-47014'
  - url: >-
      https://lore.kernel.org/linux-cve-announce/2024022831-CVE-2021-47014-ffc7@gregkh/T/#u
tags:
  - nvd
  - csaf
  - vex
  - red-hat
epss: 0.00233
epssPercentile: 0.14449
ingestedAt: '2026-08-04T10:39:39.177Z'
scores:
  nvd: 7.8
  vendor: 5.9
---

## Overview

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

net/sched: act_ct: fix wild memory access when clearing fragments

while testing re-assembly/re-fragmentation using act_ct, it's possible to
observe a crash like the following one:

 KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f]
 CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S                5.12.0-rc7+ #424
 Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017
 RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0
 Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48
 RSP: 0018:ffff888c31449db8 EFLAGS: 00010203
 RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960
 RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e
 RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350
 R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000
 R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160
 FS:  0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  <IRQ>
  inet_frag_destroy+0xa9/0x150
  call_timer_fn+0x2d/0x180
  run_timer_softirq+0x4fe/0xe70
  __do_softirq+0x197/0x5a0
  irq_exit_rcu+0x1de/0x200
  sysvec_apic_timer_interrupt+0x6b/0x80
  </IRQ>

when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb
results in putting random data in FRAG_CB(), and this causes those "wild"
memory accesses later, when the rbtree is purged. Never overwrite the skb
cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.

## Affected

- `linux_kernel >= 5.8, < 5.12.4`

## Remediation

Upgrade past the affected range:

- `linux_kernel 5.12.4`

## Vendor advisories

- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · updated 2026-09-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47014.json)