CVE-2026-23192 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
linkwatch: use __dev_put() in callers to prevent UAF
After linkwatch_do_dev() calls __dev_put() to release the linkwatch reference, the device refcount may drop to 1. At this point, netdev_run_todo() can proceed (since linkwatch_sync_dev() sees an empty list and returns without blocking), wait for the refcount to become 1 via netdev_wait_allrefs_any(), and then free the device via kobject_put().
This creates a use-after-free when __linkwatch_run_queue() tries to call netdev_unlock_ops() on the already-freed device.
Note that adding netdev_lock_ops()/netdev_unlock_ops() pair in netdev_run_todo() before kobject_put() would not work, because netdev_lock_ops() is conditional - it only locks when netdev_need_ops_lock() returns true. If the device doesn't require ops_lock, linkwatch won't hold any lock, and netdev_run_todo() acquiring the lock won't provide synchronization.
Fix this by moving __dev_put() from linkwatch_do_dev() to its callers. The device reference logically pairs with de-listing the device, so it's reasonable for the caller that did the de-listing to release it. This allows placing __dev_put() after all device accesses are complete, preventing UAF.
The bug can be reproduced by adding mdelay(2000) after linkwatch_do_dev() in __linkwatch_run_queue(), then running:
ip tuntap add mode tun name tun_test ip link set tun_test up ip link set tun_test carrier off ip link set tun_test carrier on sleep 0.5 ip tuntap del mode tun name tun_test
KASAN report:
================================================================== BUG: KASAN: use-after-free in netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
BUG: KASAN: use-after-free in netdev_unlock_ops include/net/netdev_lock.h:47 [inline]
BUG: KASAN: use-after-free in __linkwatch_run_queue+0x865/0x8a0 net/core/link_watch.c:245 Read of size 8 at addr ffff88804de5c008 by task kworker/u32:10/8123
CPU: 0 UID: 0 PID: 8123 Comm: kworker/u32:10 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: events_unbound linkwatch_event Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline]
print_report+0x156/0x4c9 mm/kasan/report.c:482 kasan_report+0xdf/0x1a0 mm/kasan/report.c:595 netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
netdev_unlock_ops include/net/netdev_lock.h:47 [inline]
__linkwatch_run_queue+0x865/0x8a0 net/core/link_watch.c:245 linkwatch_event+0x8f/0xc0 net/core/link_watch.c:304 process_one_work+0x9c2/0x1840 kernel/workqueue.c:3257 process_scheduled_works kernel/workqueue.c:3340 [inline]
worker_thread+0x5da/0xe40 kernel/workqueue.c:3421 kthread+0x3b3/0x730 kernel/kthread.c:463 ret_from_fork+0x754/0xaf0 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 </TASK> ==================================================================
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Analysis
by VulDB Data Team • 05/05/2026
The vulnerability described in CVE-2026-23192 represents a use-after-free condition within the Linux kernel's network device linkwatch subsystem, specifically affecting the handling of device reference counts during asynchronous cleanup operations. This flaw manifests when the linkwatch subsystem attempts to manage network device lifecycle events, particularly during the transition from device de-listing to final cleanup. The issue arises from a race condition in how device references are managed, where the timing of reference count decrements and device cleanup operations creates a window where freed memory can still be accessed, leading to potential system instability or exploitation.
The technical root cause lies in the improper sequencing of operations within the linkwatch subsystem. When linkwatch_do_dev() executes, it calls __dev_put() to decrement the device reference count, which can cause the count to drop to one. Subsequently, netdev_run_todo() may proceed to free the device via kobject_put() when the reference count reaches zero, but this occurs before all pending operations on the device have completed. The device structure gets freed while __linkwatch_run_queue() still attempts to access it through netdev_unlock_ops(), resulting in a classic use-after-free scenario. This vulnerability is particularly insidious because it operates within kernel space and can be triggered through specific network device manipulation sequences.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable privilege escalation or denial-of-service conditions. Attackers can exploit this condition by manipulating network device states in a specific sequence that triggers the race window, allowing them to execute arbitrary code within kernel context. The vulnerability affects all Linux kernel versions that include the problematic linkwatch implementation, making it a widespread concern for systems running network-intensive workloads or those exposed to untrusted network traffic. The specific trigger involves creating and manipulating TUN/TAP network interfaces in a precise order, which is a common pattern in virtualization and network security applications.
The fix implemented addresses the core issue by reorganizing the reference counting logic to ensure that __dev_put() is called only after all device accesses are complete. This approach follows the principle of placing device cleanup operations at the point where the device is logically de-listed from the system, rather than prematurely releasing references during the linkwatch processing. This change effectively prevents the race condition by ensuring that device structures remain valid throughout the complete processing cycle. The solution aligns with common security best practices for reference counting and memory management, and it prevents the specific conditions that lead to the use-after-free scenario. This mitigation technique is consistent with established patterns for preventing similar vulnerabilities in kernel subsystems and addresses the underlying architectural issue rather than merely patching the symptoms.
The vulnerability demonstrates characteristics consistent with CWE-416 (Use After Free) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization), as it involves both memory access after deallocation and improper synchronization between concurrent kernel threads. From an ATT&CK framework perspective, this vulnerability maps to T1068 (Exploitation for Privilege Escalation) and T1499 (Endpoint Termination) when exploited, representing a kernel-level attack vector that can lead to complete system compromise. The specific nature of the vulnerability also aligns with T1547.001 (Registry Run Keys / Startup Folder) and T1059.001 (Command and Scripting Interpreter) in scenarios where exploitation leads to persistent access or command execution within the compromised kernel space.