# CVE-2026-31771: Bluetooth: hci_event: move wake reason storage into validated event handlers

> A missing bounds check in the Linux kernel Bluetooth HCI event handler allows attackers to trigger memory corruption via short event frames.

- **Severity:** High 8.1 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-85380, BELL-CVE-2026-31771, DEBIAN-CVE-2026-31771, GHSA-pqp4-p68v-9xfr, ROOT-OS-DEBIAN-11-CVE-2026-31771, ROOT-OS-DEBIAN-12-CVE-2026-31771, ROOT-OS-DEBIAN-13-CVE-2026-31771, ROOT-OS-UBUNTU-2204-CVE-2026-31771, ROOT-OS-UBUNTU-2404-CVE-2026-31771, UBUNTU-CVE-2026-31771

## What is CVE-2026-31771?

CVE-2026-31771 is a high-severity memory corruption vulnerability in Linux kernel, published on 1 May 2026. 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: hci_event: move wake reason storage into validated event handlers

hci_store_wake_reason() is called from hci_event_packet() immediately
after stripping the HCI event header but before hci_event_func()
enforces the per-event minimum payload length from hci_ev_table.
This means a short HCI event frame can reach bacpy() before any bounds
check runs.

Rather than duplicating skb parsing and per-event length checks inside
hci_store_wake_reason(), move wake-address storage into the individual
event handlers after their existing event-length validation has
succeeded. Convert hci_store_wake_reason() into a small helper that only
stores an already-validated bdaddr while the caller holds hci_dev_lock().
Use the same helper after hci_event_func() with a NULL address to
preserve the existing unexpected-wake fallback semantics when no
validated event handler records a wake address.

Annotate the helper with __must_hold(&hdev->lock) and add
lockdep_assert_held(&hdev->lock) so future call paths keep the lock
contract explicit.

Call the helper from hci_conn_request_evt(), hci_conn_complete_evt(),
hci_sync_conn_complete_evt(), le_conn_complete_evt(),
hci_le_adv_report_evt(), hci_le_ext_adv_report_evt(),
hci_le_direct_adv_report_evt(), hci_le_pa_sync_established_evt(), and
hci_le_past_received_evt().

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-31771?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31771?

Apply the vendor's patch.

## Is CVE-2026-31771 being exploited?

There is no known exploitation of CVE-2026-31771 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31771 and fix it if it is affected.

What it is: CVE-2026-31771 is a high-severity memory corruption vulnerability in Linux kernel, published on 1 May 2026. 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-2026-31771 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31771/ (Markdown: https://insights.sbomify.com/CVE-2026-31771/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31771
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31771
- OSV: https://osv.dev/vulnerability/CVE-2026-31771

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31771/
Summaries are generated and may contain mistakes; the official description above is the record.