# CVE-2026-31773: Bluetooth: SMP: derive legacy responder STK authentication from MITM state

> Attackers can bypass Bluetooth security requirements by exploiting incorrect authentication state handling in legacy pairing, allowing unauthenticated connections.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-31773, DEBIAN-CVE-2026-31773, GHSA-vm8r-x97v-544j, ROOT-OS-DEBIAN-11-CVE-2026-31773, ROOT-OS-UBUNTU-2204-CVE-2026-31773, ROOT-OS-UBUNTU-2404-CVE-2026-31773, UBUNTU-CVE-2026-31773

## What is CVE-2026-31773?

CVE-2026-31773 is a high-severity authentication bypass 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: SMP: derive legacy responder STK authentication from MITM state

The legacy responder path in smp_random() currently labels the stored
STK as authenticated whenever pending_sec_level is BT_SECURITY_HIGH.
That reflects what the local service requested, not what the pairing
flow actually achieved.

For Just Works/Confirm legacy pairing, SMP_FLAG_MITM_AUTH stays clear
and the resulting STK should remain unauthenticated even if the local
side requested HIGH security. Use the established MITM state when
storing the responder STK so the key metadata matches the pairing result.

This also keeps the legacy path aligned with the Secure Connections code,
which already treats JUST_WORKS/JUST_CFM as unauthenticated.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-31773?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31773?

Apply the vendor's patch.

## Is CVE-2026-31773 being exploited?

There is no known exploitation of CVE-2026-31773 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-2026-31773 and fix it if it is affected.

What it is: CVE-2026-31773 is a high-severity authentication bypass 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-2026-31773 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-2026-31773/ (Markdown: https://insights.sbomify.com/CVE-2026-31773/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31773
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31773
- OSV: https://osv.dev/vulnerability/CVE-2026-31773

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31773/
Summaries are generated and may contain mistakes; the official description above is the record.