# 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.

- **Severity:** Not scored
- **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:** Yes
- **Published:** 8 Dec 2025
- **Updated:** 23 May 2026
- **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, ROOT-OS-UBUNTU-2404-CVE-2025-40308, UBUNTU-CVE-2025-40308

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40308 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2025-40308 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40308/ (Markdown: https://insights.sbomify.com/CVE-2025-40308/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40308
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40308
- OSV: https://osv.dev/vulnerability/CVE-2025-40308

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40308/
Summaries are generated and may contain mistakes; the official description above is the record.