Linux Kernel up to 6.6.127/6.12.74/6.18.15/6.19.5 xfrm_dev_unregister reference count

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4.6$0-$5k0.00

Summaryinfo

A vulnerability marked as critical has been reported in Linux Kernel up to 6.6.127/6.12.74/6.18.15/6.19.5. Affected is the function xfrm_dev_unregister. This manipulation causes reference count. This vulnerability appears as CVE-2026-43167. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.6.127/6.12.74/6.18.15/6.19.5. It has been declared as critical. Affected by this vulnerability is the function xfrm_dev_unregister. The manipulation with an unknown input leads to a reference count vulnerability. The CWE definition for the vulnerability is CWE-911. The product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. As an impact it is known to affect availability. The summary by CVE is:

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.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-43167 since 05/01/2026. The exploitation appears to be difficult. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 329305 (openSUSE 16: cluster-md-kmp-64kb / cluster-md-kmp-azure / cluster-md-kmp-default / etc (openSUSE-SU-2026:21388-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.6.128, 6.12.75, 6.18.16 or 6.19.6 eliminates this vulnerability. Applying the patch 166801e49a5b5fc127b8c9e2f110f303cfddfbc3/a3c8fede034fa27892f87c863cbd5493167d17ed/59581778792cbaf8ad788f4a21dc663ce986050e/8c75c455ecd3bfd2f36abf66edb7021c4fa19ec4/4efa91a28576054aae0e6dad9cba8fed8293aef8 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (329305). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.8
VulDB Meta Temp Score: 4.6

VulDB Base Score: 4.8
VulDB Temp Score: 4.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Reference count
CWE: CWE-911 / CWE-664
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 329305
Nessus Name: openSUSE 16: cluster-md-kmp-64kb / cluster-md-kmp-azure / cluster-md-kmp-default / etc (openSUSE-SU-2026:21388-1)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.6.128/6.12.75/6.18.16/6.19.6
Patch: 166801e49a5b5fc127b8c9e2f110f303cfddfbc3/a3c8fede034fa27892f87c863cbd5493167d17ed/59581778792cbaf8ad788f4a21dc663ce986050e/8c75c455ecd3bfd2f36abf66edb7021c4fa19ec4/4efa91a28576054aae0e6dad9cba8fed8293aef8

Timelineinfo

05/01/2026 CVE reserved
05/06/2026 +5 days Advisory disclosed
05/06/2026 +0 days VulDB entry created
07/25/2026 +80 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-43167 (🔒)
GCVE (CVE): GCVE-0-2026-43167
GCVE (VulDB): GCVE-100-361393

Entryinfo

Created: 05/06/2026 16:30
Updated: 07/25/2026 10:58
Changes: 05/06/2026 16:30 (58), 07/25/2026 10:58 (4)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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