---
id: CVE-2024-40958
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netns: Make get_net_ns() handle zero refcount net

  Syzkaller hit a warning:
  refcount_t: addition on 0; use-after-free.
  WARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 re…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netns: Make get_net_ns() handle zero refcount net

  Syzkaller hit a warning:
  refcount_t: addition on 0; use-after-free.
  WARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 re…
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-416
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.2, < 5.4.279'
  - 'linux_kernel >= 5.5, < 5.10.221'
  - 'linux_kernel >= 5.11, < 5.15.162'
  - 'linux_kernel >= 5.16, < 6.1.96'
  - 'linux_kernel >= 6.2, < 6.6.36'
  - 'linux_kernel >= 6.7, < 6.9.7'
  - linux_kernel = 6.10
patched:
  - linux_kernel 6.9.7
published: '2024-07-12'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T01:18:38.423'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2024-40958'
references:
  - url: 'https://git.kernel.org/stable/c/1b631bffcb2c09551888f3c723f4365c91fe05ef'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/2b82028a1f5ee3a8e04090776b10c534144ae77b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3a6cd326ead7c8bb1f64486789a01974a9f1ad55'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3af28df0d883e8c89a29ac31bc65f9023485743b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cb7f811f638a14590ff98f53c6dd1fb54627d940'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ef0394ca25953ea0eddcc82feae1f750451f1876'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ff960f9d3edbe08a736b5a224d91a305ccc946b0'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1b631bffcb2c09551888f3c723f4365c91fe05ef'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/2b82028a1f5ee3a8e04090776b10c534144ae77b'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/3a6cd326ead7c8bb1f64486789a01974a9f1ad55'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/3af28df0d883e8c89a29ac31bc65f9023485743b'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/cb7f811f638a14590ff98f53c6dd1fb54627d940'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/ef0394ca25953ea0eddcc82feae1f750451f1876'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://git.kernel.org/stable/c/ff960f9d3edbe08a736b5a224d91a305ccc946b0'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-265688.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-355557.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-613116.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00269
epssPercentile: 0.19
ingestedAt: '2026-10-15T03:30:12.722Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2024-09-10T17:03:35.616951Z'
---

## Overview

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

netns: Make get_net_ns() handle zero refcount net

Syzkaller hit a warning:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 refcount_warn_saturate+0xdf/0x1d0
Modules linked in:
CPU: 3 PID: 7890 Comm: tun Not tainted 6.10.0-rc3-00100-gcaa4f9578aba-dirty #310
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:refcount_warn_saturate+0xdf/0x1d0
Code: 41 49 04 31 ff 89 de e8 9f 1e cd fe 84 db 75 9c e8 76 26 cd fe c6 05 b6 41 49 04 01 90 48 c7 c7 b8 8e 25 86 e8 d2 05 b5 fe 90 <0f> 0b 90 90 e9 79 ff ff ff e8 53 26 cd fe 0f b6 1
RSP: 0018:ffff8881067b7da0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff811c72ac
RDX: ffff8881026a2140 RSI: ffffffff811c72b5 RDI: 0000000000000001
RBP: ffff8881067b7db0 R08: 0000000000000000 R09: 205b5d3730353139
R10: 0000000000000000 R11: 205d303938375420 R12: ffff8881086500c4
R13: ffff8881086500c4 R14: ffff8881086500b0 R15: ffff888108650040
FS:  00007f5b2961a4c0(0000) GS:ffff88823bd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055d7ed36fd18 CR3: 00000001482f6000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ? show_regs+0xa3/0xc0
 ? __warn+0xa5/0x1c0
 ? refcount_warn_saturate+0xdf/0x1d0
 ? report_bug+0x1fc/0x2d0
 ? refcount_warn_saturate+0xdf/0x1d0
 ? handle_bug+0xa1/0x110
 ? exc_invalid_op+0x3c/0xb0
 ? asm_exc_invalid_op+0x1f/0x30
 ? __warn_printk+0xcc/0x140
 ? __warn_printk+0xd5/0x140
 ? refcount_warn_saturate+0xdf/0x1d0
 get_net_ns+0xa4/0xc0
 ? __pfx_get_net_ns+0x10/0x10
 open_related_ns+0x5a/0x130
 __tun_chr_ioctl+0x1616/0x2370
 ? __sanitizer_cov_trace_switch+0x58/0xa0
 ? __sanitizer_cov_trace_const_cmp2+0x1c/0x30
 ? __pfx_tun_chr_ioctl+0x10/0x10
 tun_chr_ioctl+0x2f/0x40
 __x64_sys_ioctl+0x11b/0x160
 x64_sys_call+0x1211/0x20d0
 do_syscall_64+0x9e/0x1d0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5b28f165d7
Code: b3 66 90 48 8b 05 b1 48 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 48 2d 00 8
RSP: 002b:00007ffc2b59c5e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5b28f165d7
RDX: 0000000000000000 RSI: 00000000000054e3 RDI: 0000000000000003
RBP: 00007ffc2b59c650 R08: 00007f5b291ed8c0 R09: 00007f5b2961a4c0
R10: 0000000029690010 R11: 0000000000000246 R12: 0000000000400730
R13: 00007ffc2b59cf40 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
Kernel panic - not syncing: kernel: panic_on_warn set ...

This is trigger as below:
          ns0                                    ns1
tun_set_iff() //dev is tun0
   tun->dev = dev
//ip link set tun0 netns ns1
                                       put_net() //ref is 0
__tun_chr_ioctl() //TUNGETDEVNETNS
   net = dev_net(tun->dev);
   open_related_ns(&net->ns, get_net_ns); //ns1
     get_net_ns()
        get_net() //addition on 0

Use maybe_get_net() in get_net_ns in case net's ref is zero to fix this

## Affected

- `linux_kernel >= 5.2, < 5.4.279`
- `linux_kernel >= 5.5, < 5.10.221`
- `linux_kernel >= 5.11, < 5.15.162`
- `linux_kernel >= 5.16, < 6.1.96`
- `linux_kernel >= 6.2, < 6.6.36`
- `linux_kernel >= 6.7, < 6.9.7`
- `linux_kernel = 6.10`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.9.7`