# CVE-2025-39889: Bluetooth: l2cap: Check encryption key size on incoming connection

> The Linux kernel Bluetooth L2CAP module fails to enforce minimum encryption key sizes, allowing connections with weak keys that bypass security requirements.

- **Severity:** High 8.1 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **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:** 24 Sep 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-39889, DEBIAN-CVE-2025-39889, GHSA-hhgh-xj97-6f9r, ROOT-OS-UBUNTU-2404-CVE-2025-39889, UBUNTU-CVE-2025-39889

## What is CVE-2025-39889?

CVE-2025-39889 is a high-severity vulnerability in Linux kernel, published on 24 Sep 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: l2cap: Check encryption key size on incoming connection

This is required for passing GAP/SEC/SEM/BI-04-C PTS test case:
  Security Mode 4 Level 4, Responder - Invalid Encryption Key Size
  - 128 bit

This tests the security key with size from 1 to 15 bytes while the
Security Mode 4 Level 4 requests 16 bytes key size.

Currently PTS fails with the following logs:
- expected:Connection Response:
    Code: [3 (0x03)] Code
    Identifier: (lt)WildCard: Exists(gt)
    Length: [8 (0x0008)]
    Destination CID: (lt)WildCard: Exists(gt)
    Source CID: [64 (0x0040)]
    Result: [3 (0x0003)] Connection refused - Security block
    Status: (lt)WildCard: Exists(gt),
but received:Connection Response:
    Code: [3 (0x03)] Code
    Identifier: [1 (0x01)]
    Length: [8 (0x0008)]
    Destination CID: [64 (0x0040)]
    Source CID: [64 (0x0040)]
    Result: [0 (0x0000)] Connection Successful
    Status: [0 (0x0000)] No further information available

And HCI logs:
< HCI Command: Read Encrypti.. (0x05|0x0008) plen 2
        Handle: 14 Address: 00:1B:DC:F2:24:10 (Vencer Co., Ltd.)
> HCI Event: Command Complete (0x0e) plen 7
      Read Encryption Key Size (0x05|0x0008) ncmd 1
        Status: Success (0x00)
        Handle: 14 Address: 00:1B:DC:F2:24:10 (Vencer Co., Ltd.)
        Key size: 7
> ACL Data RX: Handle 14 flags 0x02 dlen 12
      L2CAP: Connection Request (0x02) ident 1 len 4
        PSM: 4097 (0x1001)
        Source CID: 64
< ACL Data TX: Handle 14 flags 0x00 dlen 16
      L2CAP: Connection Response (0x03) ident 1 len 8
        Destination CID: 64
        Source CID: 64
        Result: Connection successful (0x0000)
        Status: No further information available (0x0000)

Weakness: CWE-326 (Inadequate Encryption Strength)

## Which versions are affected by CVE-2025-39889?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39889?

Apply the vendor's patch.

## Is CVE-2025-39889 being exploited?

There is no known exploitation of CVE-2025-39889 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-2025-39889 and fix it if it is affected.

What it is: CVE-2025-39889 is a high-severity vulnerability in Linux kernel, published on 24 Sep 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-2025-39889 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-2025-39889/ (Markdown: https://insights.sbomify.com/CVE-2025-39889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39889
- OSV: https://osv.dev/vulnerability/CVE-2025-39889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39889/
Summaries are generated and may contain mistakes; the official description above is the record.