Cloudanix VulnDB

CVE-2023-53762

None

CVSS

—

EPSS

0.2%

Published

Dec 8, 2025

CISA due date

—

Cloudanix analysis

Monitor only SSVC: Track

A bug in how Linux manages Bluetooth connections could let a local attacker crash the computer or run code with higher privileges.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Moderate
Impact
Denial Of Service
Component
OS kernel
Class
Use After Free
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Use-after-free in hci_disconnect_all_sync when a Bluetooth connection object is freed by concurrent controller event processing, allowing subsequent access to freed memory in hci_set_powered_sync and related paths.

Why it matters to the business

Kernel crashes or potential memory corruption on Linux systems with Bluetooth enabled, risking denial of service or local privilege escalation; low exploitation likelihood but urgent patching needed for affected Ubuntu 20.04 LTS deployments despite the 325-day publication window.

How an attack unfolds

An attacker triggers Bluetooth connection setup and concurrent controller events that delete connections while hci_disconnect_all_sync iterates the list, resulting in access to a freed hci_conn structure; no named threat actors or ransomware campaigns observed and EPSS remains low with minimal upward trend.

How to fix it

Upgrade the Linux kernel on Ubuntu 20.04 LTS to version 5.4.0-88.99 or newer; disable Bluetooth via rfkill or kernel configuration if the feature is unused.

How to confirm the fix worked

Confirm updated kernel version with uname -r, rebuild and test Bluetooth connection workflows, and verify no KASAN reports in hci_sync.c during stress testing.

Typical attack path

  1. Initiate Bluetooth ISO or SCO connection via socket operations
  2. Trigger concurrent HCI events that invoke hci_disconn_complete_evt and free the connection
  3. Execute hci_cmd_sync_work leading to hci_set_powered_sync accessing the freed object

How to detect it

Search kernel logs and dmesg for KASAN slab-use-after-free reports referencing hci_set_powered_sync or hci_sync.c; monitor Bluetooth worker threads and hci_cmd_sync_work activity for unexpected crashes.

  • BUG: KASAN: slab-use-after-free in hci_set_powered_sync
  • hci_disconnect_all_sync
  • hci_cmd_sync_work [bluetooth]
  • kworker/u9:0

What your security team should do

  • Prioritize kernel package updates across all Ubuntu 20.04 systems within the next maintenance window
  • Temporarily disable Bluetooth services where operationally feasible
  • Add kernel crash and Bluetooth worker thread monitoring to existing SIEM rules

The record

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: Fix UAF in hci_disconnect_all_sync Use-after-free can occur in hci_disconnect_all_sync if a connection is deleted by concurrent processing of a controller event. To prevent this the code now tries to iterate over the list backwards to ensure the links are cleanup before its parents, also it no longer relies on a cursor, instead it always uses the last element since hci_abort_conn_sync is guaranteed to call hci_conn_del. UAF crash log: ================================================================== BUG: KASAN: slab-use-after-free in hci_set_powered_sync (net/bluetooth/hci_sync.c:5424) [bluetooth] Read of size 8 at addr ffff888009d9c000 by task kworker/u9:0/124 CPU: 0 PID: 124 Comm: kworker/u9:0 Tainted: G W 6.5.0-rc1+ #10 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014 Workqueue: hci0 hci_cmd_sync_work [bluetooth] Call Trace: <TASK> dump_stack_lvl+0x5b/0x90 print_report+0xcf/0x670 ? __virt_addr_valid+0xdd/0x160 ? hci_set_powered_sync+0x2c9/0x4a0 [bluetooth] kasan_report+0xa6/0xe0 ? hci_set_powered_sync+0x2c9/0x4a0 [bluetooth] ? __pfx_set_powered_sync+0x10/0x10 [bluetooth] hci_set_powered_sync+0x2c9/0x4a0 [bluetooth] ? __pfx_hci_set_powered_sync+0x10/0x10 [bluetooth] ? __pfx_lock_release+0x10/0x10 ? __pfx_set_powered_sync+0x10/0x10 [bluetooth] hci_cmd_sync_work+0x137/0x220 [bluetooth] process_one_work+0x526/0x9d0 ? __pfx_process_one_work+0x10/0x10 ? __pfx_do_raw_spin_lock+0x10/0x10 ? mark_held_locks+0x1a/0x90 worker_thread+0x92/0x630 ? __pfx_worker_thread+0x10/0x10 kthread+0x196/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2c/0x50 </TASK> Allocated by task 1782: kasan_save_stack+0x33/0x60 kasan_set_track+0x25/0x30 __kasan_kmalloc+0x8f/0xa0 hci_conn_add+0xa5/0xa80 [bluetooth] hci_bind_cis+0x881/0x9b0 [bluetooth] iso_connect_cis+0x121/0x520 [bluetooth] iso_sock_connect+0x3f6/0x790 [bluetooth] __sys_connect+0x109/0x130 __x64_sys_connect+0x40/0x50 do_syscall_64+0x60/0x90 entry_SYSCALL_64_after_hwframe+0x6e/0xd8 Freed by task 695: kasan_save_stack+0x33/0x60 kasan_set_track+0x25/0x30 kasan_save_free_info+0x2b/0x50 __kasan_slab_free+0x10a/0x180 __kmem_cache_free+0x14d/0x2e0 device_release+0x5d/0xf0 kobject_put+0xdf/0x270 hci_disconn_complete_evt+0x274/0x3a0 [bluetooth] hci_event_packet+0x579/0x7e0 [bluetooth] hci_rx_work+0x287/0xaa0 [bluetooth] process_one_work+0x526/0x9d0 worker_thread+0x92/0x630 kthread+0x196/0x1e0 ret_from_fork+0x2c/0x50 ==================================================================

Affected packages

Ecosystem Package Introduced Fixed
Linux Kernel 5.17.0 6.4.16
SUSE:Linux Enterprise High Availability Extension 15 SP6 kernel-default 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Live Patching 15 SP6 kernel-default 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Live Patching 15 SP6 kernel-livepatch-SLE15-SP6_Update_19 0 1-150600.13.3.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-64kb 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-default 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-default-base 0 6.4.0-150600.23.84.1.150600.12.38.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-docs 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-obs-build 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-source 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-syms 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server 15 SP6-LTSS kernel-zfcpdump 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-default 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-default-base 0 6.4.0-150600.23.84.1.150600.12.38.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-docs 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-obs-build 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-source 0 6.4.0-150600.23.84.1
SUSE:Linux Enterprise Server for SAP Applications 15 SP6 kernel-syms 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 dtb-aarch64 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-64kb 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-debug 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-default 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-default-base 0 6.4.0-150600.23.84.1.150600.12.38.1
openSUSE:Leap 15.6 kernel-docs 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-kvmsmall 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-obs-build 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-obs-qa 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-source 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-syms 0 6.4.0-150600.23.84.1
openSUSE:Leap 15.6 kernel-zfcpdump 0 6.4.0-150600.23.84.1

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