CVE-2026-80666 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: sco: Fix a race condition in sco_sock_timeout()
sco_sock_timeout() runs asynchronously and lock_sock(sk). If the socket is closing while the timer is running, it holds the same lock (lock_sock(sk)) twice, leading to a deadlock.
CPU 0 CPU 1 ==================== ====================== sco_sock_close() sco_sock_timeout() lock_sock(sk) // <-- LOCK __sco_sock_close() sco_chan_del() sco_conn_put() sco_conn_free() disable_delayed_work_sync() lock(sk) // <-- SAME LOCK
Fix this by moving disable_delayed_work_sync() outside of lock_sock(sk), ensuring that no lock_sock(sk) is held before sco_sock_timeout().
Lockdep splat:
WARNING: possible circular locking dependency detected 6.13.0-rc4 #7 Not tainted
syz-executor292/9514 is trying to acquire lock: ffff8881115d5070 ((work_completion)(&(&conn->timeout_work)->work)){+.+.}-{0:0}, at: rcu_lock_acquire sect/v6.13-rc4/./include/linux/rcupdate.h:337 [inline]
ffff8881115d5070 ((work_completion)(&(&conn->timeout_work)->work)){+.+.}-{0:0}, at: rcu_read_lock sect/v6.13-rc4/./include/linux/rcupdate.h:849 [inline]
ffff8881115d5070 ((work_completion)(&(&conn->timeout_work)->work)){+.+.}-{0:0}, at: start_flush_work sect/v6.13-rc4/kernel/workqueue.c:4137 [inline]
ffff8881115d5070 ((work_completion)(&(&conn->timeout_work)->work)){+.+.}-{0:0}, at: __flush_work+0xd1/0xc40 sect/v6.13-rc4/kernel/workqueue.c:4195
but task is already holding lock: ffff88807db3a258 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: lock_sock sect/v6.13-rc4/./include/net/sock.h:1623 [inline]
ffff88807db3a258 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: sco_sock_close+0x25/0x100 sect/v6.13-rc4/net/bluetooth/sco.c:524
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}:
lock_acquire+0x1c4/0x520 sect/v6.13-rc4/kernel/locking/lockdep.c:5849 lock_sock_nested+0x48/0x130 sect/v6.13-rc4/net/core/sock.c:3622 lock_sock sect/v6.13-rc4/./include/net/sock.h:1623 [inline]
sco_sock_timeout+0xbe/0x270 sect/v6.13-rc4/net/bluetooth/sco.c:158 process_one_work sect/v6.13-rc4/kernel/workqueue.c:3229 [inline]
process_scheduled_works+0xa99/0x18f0 sect/v6.13-rc4/kernel/workqueue.c:3310 worker_thread+0x8a9/0xd80 sect/v6.13-rc4/kernel/workqueue.c:3391 kthread+0x2c6/0x360 sect/v6.13-rc4/kernel/kthread.c:389 ret_from_fork+0x4e/0x80 sect/v6.13-rc4/arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 sect/v6.13-rc4/arch/x86/entry/entry_64.S:244
-> #0 ((work_completion)(&(&conn->timeout_work)->work)){+.+.}-{0:0}:
check_prev_add sect/v6.13-rc4/kernel/locking/lockdep.c:3161 [inline]
check_prevs_add sect/v6.13-rc4/kernel/locking/lockdep.c:3280 [inline]
validate_chain+0x1888/0x5760 sect/v6.13-rc4/kernel/locking/lockdep.c:3904 __lock_acquire+0x13b4/0x2120 sect/v6.13-rc4/kernel/locking/lockdep.c:5226 lock_acquire+0x1c4/0x520 sect/v6.13-rc4/kernel/locking/lockdep.c:5849 touch_work_lockdep_map sect/v6.13-rc4/kernel/workqueue.c:3909 [inline]
start_flush_work sect/v6.13-rc4/kernel/workqueue.c:4163 [inline]
__flush_work+0x70f/0xc40 sect/v6.13-rc4/kernel/workqueue.c:4195 __cancel_work_sync sect/v6.13-rc4/kernel/workqueue.c:4351 [inline]
disable_delayed_work_sync+0xbb/0xf0 sect/v6.13-rc4/kernel/workqueue.c:4514 sco_conn_free sect/v6.13-rc4/net/bluetooth/sco.c:95 [inline]
kref_put sect/v6.13-rc4/./include/linux/kref.h:65 [inline]
sco_conn_put+0x18f/0x270 sect/v6.13-rc4/net/bluetooth/sco.c:107 sco_chan_del+0xe2/0x210 sect/v6.13-rc4/net/bluetooth/sco.c:236 sco_sock_close+0x8f/0x100 sect/v6.13-rc4/net/bluetooth/sco.c:526 sco_sock_release+0x62/0x2d0 sect/v6.13-rc4/net/blueto ---truncated---
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel Bluetooth subsystem contains a critical concurrency flaw within the SCO socket implementation, specifically in the interaction between connection closure and timeout handling mechanisms. This vulnerability manifests as a deadlock caused by improper lock ordering when managing asynchronous work items alongside socket state transitions. The core issue resides in the sco_sock_timeout function, which is designed to run asynchronously via a delayed work queue to handle connection timeouts. Under normal operation, this function acquires the socket lock using lock_sk before performing its checks and cleanup tasks. However, during the process of closing an SCO socket through sco_sock_close, the kernel attempts to clean up associated resources by calling disable_delayed_work_sync on the timeout worker. This synchronization call requires acquiring a work completion lock that is internally dependent on the same socket lock already held by the close routine. Consequently, when the timer expires while the socket is being closed, two execution contexts contend for these interdependent locks in an incompatible order, resulting in a circular locking dependency and immediate system deadlock.
From a technical perspective, this flaw represents a classic race condition arising from inconsistent lock acquisition patterns across different code paths that operate on shared kernel objects. The vulnerability allows any local user with the ability to create or manipulate Bluetooth SCO sockets to trigger the conflicting state transition. By rapidly opening and closing connections while simultaneously inducing timeout conditions, an attacker can force the kernel into holding both locks simultaneously in a cyclic dependency chain. This leads to a denial of service condition where the affected CPU core becomes permanently blocked waiting for lock release that will never occur due to the circular wait. The impact is severe as it compromises system stability and availability without requiring elevated privileges or remote network access, relying instead on local interaction with Bluetooth stack interfaces.
This vulnerability aligns with CWE-833 Lock Inversion, a category of concurrency errors where locks are acquired in an inconsistent order across different execution paths, leading to deadlocks. It also relates closely to CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization, as the race condition stems from inadequate synchronization between the socket closure path and the asynchronous timeout handler. In terms of adversary tactics, this flaw can be leveraged within MITRE ATT&CK technique T1499 Endpoint Denial of Service, where an attacker exhausts system resources or stability to disrupt normal operations. The specific mechanism involves exploiting kernel-level locking logic failures rather than resource exhaustion through volume, making it a precise structural weakness in the driver implementation.
Mitigation strategies primarily involve applying vendor-provided patches that restructure the lock acquisition sequence within the sco_sock_close and related functions. The definitive fix requires moving the disable_delayed_work_sync call outside of the critical section protected by lock_sk to prevent holding multiple locks with conflicting dependency orders simultaneously. System administrators should ensure their kernels are updated to versions where this locking hierarchy has been corrected, typically available through standard distribution security updates for affected Linux releases. Additionally, developers reviewing similar Bluetooth or network socket implementations should audit all asynchronous work handlers that interact with closing sockets to verify consistent lock ordering and avoid nested acquisitions of interdependent mutexes.