CVE-2025-39981
Description
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: MGMT: Fix possible UAFs
This attemps to fix possible UAFs caused by struct mgmt_pending being freed while still being processed like in the following trace, in order to fix mgmt_pending_valid is introduce and use to check if the mgmt_pending hasn't been removed from the pending list, on the complete callbacks it is used to check and in addtion remove the cmd from the list while holding mgmt_pending_lock to avoid TOCTOU problems since if the cmd is left on the list it can still be accessed and freed.
BUG: KASAN: slab-use-after-free in mgmt_add_adv_patterns_monitor_sync+0x35/0x50 net/bluetooth/mgmt.c:5223 Read of size 8 at addr ffff8880709d4dc0 by task kworker/u11:0/55
CPU: 0 UID: 0 PID: 55 Comm: kworker/u11:0 Not tainted 6.16.4 #2 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 Workqueue: hci0 hci_cmd_sync_work Call Trace:
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xca/0x240 mm/kasan/report.c:482 kasan_report+0x118/0x150 mm/kasan/report.c:595 mgmt_add_adv_patterns_monitor_sync+0x35/0x50 net/bluetooth/mgmt.c:5223 hci_cmd_sync_work+0x210/0x3a0 net/bluetooth/hci_sync.c:332 process_one_work kernel/workqueue.c:3238 [inline] process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3321 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402 kthread+0x711/0x8a0 kernel/kthread.c:464 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 home/kwqcheii/source/fuzzing/kernel/kasan/linux-6.16.4/arch/x86/entry/entry_64.S:245
Allocated by task 12210: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:377 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394 kasan_kmalloc include/linux/kasan.h:260 [inline] __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4364 kmalloc_noprof include/linux/slab.h:905 [inline] kzalloc_noprof include/linux/slab.h:1039 [inline] mgmt_pending_new+0x65/0x1e0 net/bluetooth/mgmt_util.c:269 mgmt_pending_add+0x35/0x140 net/bluetooth/mgmt_util.c:296 __add_adv_patterns_monitor+0x130/0x200 net/bluetooth/mgmt.c:5247 add_adv_patterns_monitor+0x214/0x360 net/bluetooth/mgmt.c:5364 hci_mgmt_cmd+0x9c9/0xef0 net/bluetooth/hci_sock.c:1719 hci_sock_sendmsg+0x6ca/0xef0 net/bluetooth/hci_sock.c:1839 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x219/0x270 net/socket.c:729 sock_write_iter+0x258/0x330 net/socket.c:1133 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 12221: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576 poison_slab_object mm/kasan/common.c:247 [inline] __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264 kasan_slab_free include/linux/kasan.h:233 [inline] slab_free_hook mm/slub.c:2381 [inline] slab_free mm/slub.c:4648 [inline] kfree+0x18e/0x440 mm/slub.c:4847 mgmt_pending_free net/bluetooth/mgmt_util.c:311 [inline] mgmt_pending_foreach+0x30d/0x380 net/bluetooth/mgmt_util.c:257 __mgmt_power_off+0x169/0x350 net/bluetooth/mgmt.c:9444 hci_dev_close_sync+0x754/0x1330 net/bluetooth/hci_sync.c:5290 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline] hci_dev_close+0x108/0x200 net/bluetooth/hci_core.c:526 sock_do_ioctl+0xd9/0x300 net/socket.c:1192 sock_ioctl+0x576/0x790 net/socket.c:1313 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xf ---truncated---
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
CVE-2025-39981 is a use-after-free vulnerability in the Linux kernel's Bluetooth MGMT subsystem where pending commands can be freed while still being processed, leading to memory corruption.
Root
Cause
CVE-2025-39981 describes a use-after-free (UAF) flaw in the Linux kernel's Bluetooth Management (MGMT) interface. The issue arises because struct mgmt_pending objects can be freed from the pending list while a completion callback is still accessing them, as illustrated by the KASAN report showing a slab-use-after-free in mgmt_add_adv_patterns_monitor_sync [1]. The root cause is a missing synchronization between the command submission path and its completion, allowing the pending entry to be released before the synchronous handler finishes using it.
Exploitation
The vulnerability is triggered through a race condition between a user-space MGMT command (e.g., adding an advertisement pattern monitor) and the kernel's completion handling in hci_cmd_sync_work. An attacker with local access and the CAP_NET_ADMIN capability (or Bluetooth configuration rights) could send a carefully timed sequence of MGMT requests to cause a freed pending command to be dereferenced during processing [2]. No physical proximity is required if the host has Bluetooth hardware and the MGMT socket is accessible.
Impact
A successful exploit could lead to memory corruption, potentially allowing an attacker to crash the system (denial of service) or escalate privileges by controlling the freed memory contents. The KASAN report confirms a read-after-free on a kmalloc-allocated slab, which can be leveraged to hijack control flow or leak sensitive kernel information.
Mitigation
The fix introduces mgmt_pending_valid() and acquires mgmt_pending_lock in completion callbacks to ensure the pending command is still on the list before accessing it, preventing the UAF [1][2]. Patches are already merged into the stable kernel branches and should be applied to all affected systems, particularly those using Bluetooth functionality.
AI Insight generated on May 19, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
1Patches
3302a1f674c00d71b98f253b087a1f16f07c6Vulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
4News mentions
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