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Fencer Vulns
medium 5.5

CVE-2026-43167 json

xfrm: always flush state and policy upon NETDEV_UNREGISTER event

published 2026-05-06 6 mo ago modified 2026-11-06 2 d ago also EUVD-2026-27728

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits
0
none known

Summary

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

xfrm: always flush state and policy upon NETDEV_UNREGISTER event

syzbot is reporting that "struct xfrm_state" refcount is leaking.

unregister_netdevice: waiting for netdevsim0 to become free. Usage count = 2 ref_tracker: netdev@ffff888052f24618 has 1/1 users at __netdev_tracker_alloc include/linux/netdevice.h:4400 [inline] netdev_tracker_alloc include/linux/netdevice.h:4412 [inline] xfrm_dev_state_add+0x3a5/0x1080 net/xfrm/xfrm_device.c:316 xfrm_state_construct net/xfrm/xfrm_user.c:986 [inline] xfrm_add_sa+0x34ff/0x5fa0 net/xfrm/xfrm_user.c:1022 xfrm_user_rcv_msg+0x58e/0xc00 net/xfrm/xfrm_user.c:3507 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2550 xfrm_netlink_rcv+0x71/0x90 net/xfrm/xfrm_user.c:3529 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x8c8/0xdd0 net/netlink/af_netlink.c:1894 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg net/socket.c:742 [inline] ____sys_sendmsg+0xa5d/0xc30 net/socket.c:2592 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2646 __sys_sendmsg+0x16d/0x220 net/socket.c:2678 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f

This is because commit d77e38e612a0 ("xfrm: Add an IPsec hardware offloading API") implemented xfrm_dev_unregister() as no-op despite xfrm_dev_state_add() from xfrm_state_construct() acquires a reference to "struct net_device". I guess that that commit expected that NETDEV_DOWN event is fired before NETDEV_UNREGISTER event fires, and also assumed that xfrm_dev_state_add() is called only if (dev->features & NETIF_F_HW_ESP) != 0.

Sabrina Dubroca identified steps to reproduce the same symptoms as below.

echo 0 > /sys/bus/netdevsim/new_device dev=$(ls -1 /sys/bus/netdevsim/devices/netdevsim0/net/) ip xfrm state add src 192.168.13.1 dst 192.168.13.2 proto esp \ spi 0x1000 mode tunnel aead 'rfc4106(gcm(aes))' $key 128 \ offload crypto dev $dev dir out ethtool -K $dev esp-hw-offload off echo 0 > /sys/bus/netdevsim/del_device

Like these steps indicate, the NETIF_F_HW_ESP bit can be cleared after xfrm_dev_state_add() acquired a reference to "struct net_device". Also, xfrm_dev_state_add() does not check for the NETIF_F_HW_ESP bit when acquiring a reference to "struct net_device".

Commit 03891f820c21 ("xfrm: handle NETDEV_UNREGISTER for xfrm device") re-introduced the NETDEV_UNREGISTER event to xfrm_dev_event(), but that commit for unknown reason chose to share xfrm_dev_down() between the NETDEV_DOWN event and the NETDEV_UNREGISTER event. I guess that that commit missed the behavior in the previous paragraph.

Therefore, we need to re-introduce xfrm_dev_unregister() in order to release the reference to "struct net_device" by unconditionally flushing state and policy.

Patch / fix

  • Linux Linux 6.1.191, 6.6.128, 6.12.75, 6.18.16, 6.19.6, 7.0
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.19.6-1

debian advisories DEBIAN-CVE-2026-43167

  • linux Ubuntu 24.04 LTS 6.8.0-134.134
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1060.63
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1063.69
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1058.64
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1060.61
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1063.71
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1045.48
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1060.64

ubuntu advisories UBUNTU-CVE-2026-43167

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-source Linux Micro 6.1, Linux Micro 6.0 6.4.0-50.2
  • kernel-default Linux Micro 6.1, Linux Micro 6.0 6.4.0-50.1
  • kernel-kvmsmall Linux Micro 6.1, Linux Micro 6.0 6.4.0-50.1
  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-50.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-50.2
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.73.2
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.73.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.73.2

suse advisories SUSE-SU-2026:22810-1SUSE-SU-2026:22809-1SUSE-SU-2026:22904-1SUSE-SU-2026:22903-1SUSE-SU-2026:3166-1SUSE-SU-2026:22742-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.36.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.36.1

opensuse advisories openSUSE-SU-2026:21388-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-43167 updated cvss 5.5

kernel: xfrm: always flush state and policy upon NETDEV_UNREGISTER event

  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 d ago

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.