CVE-2026-23167 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
nfc: nci: Fix race between rfkill and nci_unregister_device().
syzbot reported the splat below [0] without a repro.
It indicates that struct nci_dev.cmd_wq had been destroyed before nci_close_device() was called via rfkill.
nci_dev.cmd_wq is only destroyed in nci_unregister_device(), which (I think) was called from virtual_ncidev_close() when syzbot close()d an fd of virtual_ncidev.
The problem is that nci_unregister_device() destroys nci_dev.cmd_wq first and then calls nfc_unregister_device(), which removes the device from rfkill by rfkill_unregister().
So, the device is still visible via rfkill even after nci_dev.cmd_wq is destroyed.
Let's unregister the device from rfkill first in nci_unregister_device().
Note that we cannot call nfc_unregister_device() before nci_close_device() because
1) nfc_unregister_device() calls device_del() which frees all memory allocated by devm_kzalloc() and linked to ndev->conn_info_list
2) nci_rx_work() could try to queue nci_conn_info to ndev->conn_info_list which could be leaked
Thus, nfc_unregister_device() is split into two functions so we can remove rfkill interfaces only before nci_close_device().
[0]:
DEBUG_LOCKS_WARN_ON(1) WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:238 [inline], CPU#0: syz.0.8675/6349
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4854 [inline], CPU#0: syz.0.8675/6349
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x39d/0x2cf0 kernel/locking/lockdep.c:5187, CPU#0: syz.0.8675/6349 Modules linked in: CPU: 0 UID: 0 PID: 6349 Comm: syz.0.8675 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026 RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4854 [inline]
RIP: 0010:__lock_acquire+0x3a4/0x2cf0 kernel/locking/lockdep.c:5187 Code: 18 00 4c 8b 74 24 08 75 27 90 e8 17 f2 fc 02 85 c0 74 1c 83 3d 50 e0 4e 0e 00 75 13 48 8d 3d 43 f7 51 0e 48 c7 c6 8b 3a de 8d <67> 48 0f b9 3a 90 31 c0 0f b6 98 c4 00 00 00 41 8b 45 20 25 ff 1f RSP: 0018:ffffc9000c767680 EFLAGS: 00010046 RAX: 0000000000000001 RBX: 0000000000040000 RCX: 0000000000080000 RDX: ffffc90013080000 RSI: ffffffff8dde3a8b RDI: ffffffff8ff24ca0 RBP: 0000000000000003 R08: ffffffff8fef35a3 R09: 1ffffffff1fde6b4 R10: dffffc0000000000 R11: fffffbfff1fde6b5 R12: 00000000000012a2 R13: ffff888030338ba8 R14: ffff888030338000 R15: ffff888030338b30 FS: 00007fa5995f66c0(0000) GS:ffff8881256f8000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f7e72f842d0 CR3: 00000000485a0000 CR4: 00000000003526f0 Call Trace: <TASK> lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868 touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:3940 __flush_workqueue+0x14b/0x14f0 kernel/workqueue.c:3982 nci_close_device+0x302/0x630 net/nfc/nci/core.c:567 nci_dev_down+0x3b/0x50 net/nfc/nci/core.c:639 nfc_dev_down+0x152/0x290 net/nfc/core.c:161 nfc_rfkill_set_block+0x2d/0x100 net/nfc/core.c:179 rfkill_set_block+0x1d2/0x440 net/rfkill/core.c:346 rfkill_fop_write+0x461/0x5a0 net/rfkill/core.c:1301 vfs_write+0x29a/0xb90 fs/read_write.c:684 ksys_write+0x150/0x270 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fa59b39acb9 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fa5995f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fa59b615fa0 RCX: 00007fa59b39acb9 RDX: 0000000000000008 RSI: 0000200000000080 RDI: 0000000000000007 RBP: 00007fa59b408bf7 R08: ---truncated---
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Analysis
by VulDB Data Team • 05/05/2026
The vulnerability CVE-2026-23167 resides within the Linux kernel's NFC (Near Field Communication) subsystem, specifically in the NCI (NFC Controller Interface) layer. This issue manifests as a race condition between the rfkill subsystem and the nci_unregister_device() function, which can lead to a use-after-free scenario. The vulnerability was identified through syzbot, an automated fuzzer, which reported a kernel oops without a clear reproduction case. The root cause lies in the improper ordering of operations during device cleanup, where the command workqueue (cmd_wq) of the NFC device is destroyed before the rfkill interface is properly unregistered, leading to a potential kernel crash when rfkill attempts to access freed memory structures.
The technical flaw occurs in the nci_unregister_device() function where the sequence of operations creates a temporal gap between the destruction of the nci_dev.cmd_wq workqueue and the removal of the device from rfkill management. When rfkill attempts to process a device down event, it tries to access the already destroyed cmd_wq, resulting in a kernel lockdep warning and potential system instability. This race condition is particularly dangerous because it can be triggered through the virtual NFC device interface, where syzbot closes file descriptors, causing virtual_ncidev_close() to invoke nci_unregister_device(). The current implementation destroys cmd_wq first and then calls nfc_unregister_device(), which removes the device from rfkill management, but this ordering creates a window where the device is no longer accessible to rfkill while its memory structures are still being accessed.
The operational impact of this vulnerability extends beyond simple system crashes to potential security implications within NFC device management and kernel memory corruption. Attackers could potentially exploit this race condition to cause denial of service or, in more sophisticated scenarios, achieve privilege escalation through controlled memory corruption. The vulnerability affects systems utilizing NFC hardware with NCI controllers and demonstrates a classic race condition pattern that aligns with CWE-362, which describes concurrent execution with race conditions. The issue is particularly concerning in embedded systems and mobile platforms where NFC functionality is prevalent, as these environments often handle sensitive data transactions and may be targeted for exploitation.
Mitigation strategies for CVE-2026-23167 require careful modification of the device cleanup sequence within the NFC subsystem. The solution involves splitting the nfc_unregister_device() function into two distinct operations, ensuring that rfkill interfaces are unregistered before nci_close_device() is called, thereby preventing access to freed memory structures. This approach aligns with ATT&CK technique T1068, which involves exploiting weaknesses in the system to gain privileges, by addressing the underlying memory management flaw that could be leveraged for privilege escalation. System administrators should ensure that all Linux kernel updates are applied promptly, particularly those containing the patched NFC subsystem code, and implement monitoring for kernel oops or lockdep warnings related to NFC device management. Additionally, security teams should consider the broader implications of NFC subsystem vulnerabilities in environments where NFC is used for payment processing or secure access control, as this vulnerability could potentially be combined with other exploits to compromise system integrity. The fix specifically addresses the improper synchronization between NFC device cleanup and rfkill management, reducing the attack surface for potential exploitation while maintaining the intended functionality of the NFC subsystem.