CVE-2026-23146 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: hci_uart: fix null-ptr-deref in hci_uart_write_work
hci_uart_set_proto() sets HCI_UART_PROTO_INIT before calling hci_uart_register_dev(), which calls proto->open() to initialize hu->priv. However, if a TTY write wakeup occurs during this window, hci_uart_tx_wakeup() may schedule write_work before hu->priv is initialized, leading to a NULL pointer dereference in hci_uart_write_work() when proto->dequeue() accesses hu->priv.
The race condition is:
CPU0 CPU1 ---- ---- hci_uart_set_proto() set_bit(HCI_UART_PROTO_INIT) hci_uart_register_dev() tty write wakeup hci_uart_tty_wakeup() hci_uart_tx_wakeup() schedule_work(&hu->write_work) proto->open(hu) // initializes hu->priv hci_uart_write_work() hci_uart_dequeue() proto->dequeue(hu) // accesses hu->priv (NULL!)
Fix this by moving set_bit(HCI_UART_PROTO_INIT) after proto->open() succeeds, ensuring hu->priv is initialized before any work can be scheduled.
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Analysis
by VulDB Data Team • 03/18/2026
The vulnerability described in CVE-2026-23146 represents a critical race condition within the Linux kernel's Bluetooth subsystem, specifically affecting the hci_uart driver component. This flaw exists in the Bluetooth HCI (Host Controller Interface) UART communication layer that handles serial communication between Bluetooth host controllers and the system. The issue manifests as a null pointer dereference that can lead to system instability and potential denial of service conditions. The vulnerability is particularly concerning because it occurs during the initialization phase of Bluetooth UART devices, making it exploitable during normal system operation when Bluetooth functionality is being activated.
The technical implementation of this vulnerability stems from improper ordering of operations during the Bluetooth device initialization sequence. The race condition occurs when the kernel attempts to set up a Bluetooth UART device through the hci_uart_set_proto() function. During this process, the system sets the HCI_UART_PROTO_INIT bit to indicate protocol initialization, but this occurs before the protocol's open function completes and initializes the device private data structure hu->priv. This timing issue creates a window where a TTY write wakeup event can occur, causing the system to schedule write_work before the private data structure is properly initialized. The CWE-362 reference applies here as this represents a classic race condition where concurrent operations access shared resources without proper synchronization, leading to unpredictable behavior and potential system crashes.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise the overall stability of Linux-based systems that utilize Bluetooth functionality. When the race condition occurs, the hci_uart_write_work() function attempts to access hu->priv which remains NULL, causing an immediate kernel panic or system lockup. This affects systems where Bluetooth is enabled, particularly those using Bluetooth UART interfaces such as USB Bluetooth adapters, embedded Bluetooth modules, or systems with built-in Bluetooth capabilities. The vulnerability can be triggered during normal system operation when Bluetooth devices are being initialized or when write operations occur during the brief initialization window. From an ATT&CK framework perspective, this represents a privilege escalation vector through system instability, potentially enabling attackers to cause persistent denial of service conditions or force system reboots.
The fix implemented for this vulnerability involves a simple but crucial reordering of initialization steps. By moving the set_bit(HCI_UART_PROTO_INIT) operation to occur after the proto->open() function successfully completes and initializes hu->priv, the system ensures that all subsequent operations have access to properly initialized data structures. This approach eliminates the race condition by establishing proper ordering semantics that guarantee data availability before any asynchronous work can be scheduled. The solution aligns with established kernel development practices for handling race conditions and demonstrates the importance of careful initialization ordering in concurrent systems. This mitigation strategy prevents the null pointer dereference by ensuring that the device private data structure is fully populated before any potential work scheduling can occur, thereby maintaining system stability and preventing the exploitation of this timing vulnerability.