CVE-2025-40308 Bluetooth: bcsp: receive data only if registered
A local attacker can trigger a kernel crash via Bluetooth UART data when the protocol is unregistered, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40308?
CVE-2025-40308 is a vulnerability in Linux, published on 8 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: bcsp: receive data only if registered
Currently, bcsp_recv() can be called even when the BCSP protocol has not been registered. This leads to a NULL pointer dereference, as shown in the following stack trace:
KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f] RIP: 0010:bcsp_recv+0x13d/0x1740 drivers/bluetooth/hci_bcsp.c:590 Call Trace: <TASK> hci_uart_tty_receive+0x194/0x220 drivers/bluetooth/hci_ldisc.c:627 tiocsti+0x23c/0x2c0 drivers/tty/tty_io.c:2290 tty_ioctl+0x626/0xde0 drivers/tty/tty_io.c:2706 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893 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
To prevent this, ensure that the HCI_UART_REGISTERED flag is set before processing received data. If the protocol is not registered, return -EUNATCH.
Which versions are affected by CVE-2025-40308?
How do I fix CVE-2025-40308?
Apply the vendor's patch.
Is CVE-2025-40308 being exploited?
There is no known exploitation of CVE-2025-40308 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40308, DEBIAN-CVE-2025-40308, GHSA-4r3x-4wj9-mxfm, ROOT-OS-DEBIAN-12-CVE-2025-40308, ROOT-OS-DEBIAN-13-CVE-2025-40308, ROOT-OS-UBUNTU-2204-CVE-2025-40308 and 2 more.