# CVE-2021-34981: Linux Kernel Bluetooth CMTP Module Double Free Privilege Escalation Vulnerability

> Local attackers can escalate privileges and execute kernel code via a double free vulnerability in the Linux Kernel Bluetooth CMTP module.

- **Severity:** High 7.5 (`CVSS:3.0/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 May 2024
- **Updated:** 4 Aug 2024
- **Also known as:** CVE-2021-3534, DEBIAN-CVE-2021-34981, GHSA-98qh-xfx7-vfqv, UBUNTU-CVE-2021-34981

## What is CVE-2021-34981?

CVE-2021-34981 is a high-severity use after free vulnerability in Linux kernel, published on 7 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Linux Kernel Bluetooth CMTP Module Double Free Privilege Escalation Vulnerability. This vulnerability allows local attackers to escalate privileges on affected installations of Linux Kernel. An attacker must first obtain the ability to execute high-privileged code on the target system in order to exploit this vulnerability.

The specific flaw exists within the CMTP module. The issue results from the lack of validating the existence of an object prior to performing further free operations on the object. An attacker can leverage this vulnerability to escalate privileges and execute code in the context of the kernel. Was ZDI-CAN-11977.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2021-34981?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-34981?

Apply the vendor's patch.

## Is CVE-2021-34981 being exploited?

There is no known exploitation of CVE-2021-34981 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-2021-34981 and fix it if it is affected.

What it is: CVE-2021-34981 is a high-severity use after free vulnerability in Linux kernel, published on 7 May 2024. 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-2021-34981 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-2021-34981/ (Markdown: https://insights.sbomify.com/CVE-2021-34981/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34981
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34981
- OSV: https://osv.dev/vulnerability/CVE-2021-34981

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34981/
Summaries are generated and may contain mistakes; the official description above is the record.