CVE-2023-53673 in Linux
Summary
by MITRE • 10/07/2025
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_event: call disconnect callback before deleting conn
In hci_cs_disconnect, we do hci_conn_del even if disconnection failed.
ISO, L2CAP and SCO connections refer to the hci_conn without hci_conn_get, so disconn_cfm must be called so they can clean up their conn, otherwise use-after-free occurs.
ISO: ========================================================== iso_sock_connect:880: sk 00000000eabd6557 iso_connect_cis:356: 70:1a:b8:98:ff:a2 -> 28:3d:c2:4a:7e:da ... iso_conn_add:140: hcon 000000001696f1fd conn 00000000b6251073 hci_dev_put:1487: hci0 orig refcnt 17 __iso_chan_add:214: conn 00000000b6251073 iso_sock_clear_timer:117: sock 00000000eabd6557 state 3 ... hci_rx_work:4085: hci0 Event packet hci_event_packet:7601: hci0: event 0x0f hci_cmd_status_evt:4346: hci0: opcode 0x0406 hci_cs_disconnect:2760: hci0: status 0x0c hci_sent_cmd_data:3107: hci0 opcode 0x0406 hci_conn_del:1151: hci0 hcon 000000001696f1fd handle 2560 hci_conn_unlink:1102: hci0: hcon 000000001696f1fd hci_conn_drop:1451: hcon 00000000d8521aaf orig refcnt 2 hci_chan_list_flush:2780: hcon 000000001696f1fd hci_dev_put:1487: hci0 orig refcnt 21 hci_dev_put:1487: hci0 orig refcnt 20 hci_req_cmd_complete:3978: opcode 0x0406 status 0x0c ... <no iso_* activity on sk/conn> ... iso_sock_sendmsg:1098: sock 00000000dea5e2e0, sk 00000000eabd6557 BUG: kernel NULL pointer dereference, address: 0000000000000668 PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014 RIP: 0010:iso_sock_sendmsg (net/bluetooth/iso.c:1112) bluetooth ==========================================================
L2CAP: ================================================================== hci_cmd_status_evt:4359: hci0: opcode 0x0406 hci_cs_disconnect:2760: hci0: status 0x0c hci_sent_cmd_data:3085: hci0 opcode 0x0406 hci_conn_del:1151: hci0 hcon ffff88800c999000 handle 3585 hci_conn_unlink:1102: hci0: hcon ffff88800c999000 hci_chan_list_flush:2780: hcon ffff88800c999000 hci_chan_del:2761: hci0 hcon ffff88800c999000 chan ffff888018ddd280 ... BUG: KASAN: slab-use-after-free in hci_send_acl+0x2d/0x540 [bluetooth]
Read of size 8 at addr ffff888018ddd298 by task bluetoothd/1175
CPU: 0 PID: 1175 Comm: bluetoothd Tainted: G E 6.4.0-rc4+ #2 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x5b/0x90 print_report+0xcf/0x670 ? __virt_addr_valid+0xf8/0x180 ? hci_send_acl+0x2d/0x540 [bluetooth]
kasan_report+0xa8/0xe0 ? hci_send_acl+0x2d/0x540 [bluetooth]
hci_send_acl+0x2d/0x540 [bluetooth]
? __pfx___lock_acquire+0x10/0x10 l2cap_chan_send+0x1fd/0x1300 [bluetooth]
? l2cap_sock_sendmsg+0xf2/0x170 [bluetooth]
? __pfx_l2cap_chan_send+0x10/0x10 [bluetooth]
? lock_release+0x1d5/0x3c0 ? mark_held_locks+0x1a/0x90 l2cap_sock_sendmsg+0x100/0x170 [bluetooth]
sock_write_iter+0x275/0x280 ? __pfx_sock_write_iter+0x10/0x10 ? __pfx___lock_acquire+0x10/0x10 do_iter_readv_writev+0x176/0x220 ? __pfx_do_iter_readv_writev+0x10/0x10 ? find_held_lock+0x83/0xa0 ? selinux_file_permission+0x13e/0x210 do_iter_write+0xda/0x340 vfs_writev+0x1b4/0x400 ? __pfx_vfs_writev+0x10/0x10 ? __seccomp_filter+0x112/0x750 ? populate_seccomp_data+0x182/0x220 ? __fget_light+0xdf/0x100 ? do_writev+0x19d/0x210 do_writev+0x19d/0x210 ? __pfx_do_writev+0x10/0x10 ? mark_held_locks+0x1a/0x90 do_syscall_64+0x60/0x90 ? lockdep_hardirqs_on_prepare+0x149/0x210 ? do_syscall_64+0x6c/0x90 ? lockdep_hardirqs_on_prepare+0x149/0x210 entry_SYSCALL_64_after_hwframe+0x72/0xdc RIP: 0033:0x7ff45cb23e64 Code: 15 d1 1f 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 f3 0f 1e fa 80 3d 9d a7 0d 00 00 74 13 b8 14 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 89 54 24 1c 48 89 RSP: 002b:00007fff21ae09b8 EFLAGS: 00000202 ORIG_RAX: 0000000000000014 RAX: ffffffffffffffda RBX: ---truncated---
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Analysis
by VulDB Data Team • 03/01/2026
The vulnerability described in CVE-2023-53673 resides within the Linux kernel's Bluetooth subsystem, specifically in how the HCI (Host Controller Interface) layer handles disconnection events for Bluetooth connections. This flaw manifests as a use-after-free condition that arises when the hci_conn_del function is invoked even in cases where the disconnection command fails. The root cause lies in the improper sequencing of operations during disconnection, where the disconnect callback is not executed before the connection object is deleted. This sequence error leads to scenarios where L2CAP, ISO, and SCO connection handlers attempt to access connection objects that have already been freed, resulting in kernel crashes or potential exploitation.
The technical nature of this vulnerability aligns with CWE-416, which describes the use of freed memory condition, and it directly impacts the kernel's memory management and synchronization mechanisms. The issue occurs during the hci_cs_disconnect function execution, where the system attempts to delete a connection object without first notifying the associated connection handlers to clean up their references. This is particularly problematic for ISO (Individual Stream Optimization) and L2CAP (Logical Link Control and Adaptation Protocol) connections, which maintain references to the hci_conn structure through various socket and channel mechanisms. The kernel's Bluetooth subsystem relies on proper reference counting and callback mechanisms to ensure that connection resources are not prematurely deallocated while still being accessed by active processes.
The operational impact of this vulnerability is significant, as it can lead to system crashes through kernel NULL pointer dereferences or more severe exploitation opportunities. When the disconnect command fails with status code 0x0c (which indicates a "Connection Failed" condition), the system proceeds to delete the connection object without ensuring that all dependent handlers have been notified to release their references. This results in scenarios where subsequent operations on the connection, such as sending data through iso_sock_sendmsg or hci_send_acl, attempt to access freed memory locations. The crash traces show that processes like bluetoothd can trigger these conditions when attempting to send data over already disconnected but not properly cleaned-up connections, leading to kernel oops and system instability. The vulnerability is particularly concerning because it affects core Bluetooth functionality and can potentially be exploited to cause denial of service or, in more sophisticated scenarios, achieve privilege escalation through controlled memory corruption.
Mitigation strategies for CVE-2023-53673 should focus on ensuring proper callback execution before connection object deletion. The fix involves modifying the hci_cs_disconnect function to invoke the disconn_cfm callback before calling hci_conn_del, thereby allowing all connection handlers to properly clean up their references. This approach aligns with ATT&CK technique T1068, which involves exploiting local privilege escalation vulnerabilities, and ensures proper resource management during connection lifecycle operations. System administrators should update their kernels to versions that include the patched Bluetooth subsystem code, which implements the corrected sequence of operations. Additionally, monitoring for unusual Bluetooth disconnection patterns and implementing proper kernel hardening measures can help detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of proper synchronization and resource management in kernel subsystems, particularly those handling network protocols where multiple components maintain references to shared resources.