# CVE-2021-3640: Use after free in kernel

> A local privileged user can exploit a use-after-free race condition in the Linux kernel HCI subsystem to crash the system or escalate privileges.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 3 Mar 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3640, GHSA-c8w8-4f3f-5v3j, OESA-2021-1336, UBUNTU-CVE-2021-3640

## What is CVE-2021-3640?

CVE-2021-3640 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 3 Mar 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw use-after-free in function sco_sock_sendmsg() of the Linux kernel HCI subsystem was found in the way user calls ioct UFFDIO_REGISTER or other way triggers race condition of the call sco_conn_del() together with the call sco_sock_sendmsg() with the expected controllable faulting memory page. A privileged local user could use this flaw to crash the system or escalate their privileges on the system.

Weakness: CWE-416 (Use After Free), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2021-3640?

It affects 12 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux, Fedoraproject Fedora, Linux kernel, Netapp H300e Firmware, Netapp H300s Firmware, Netapp H410c Firmware, Netapp H410s Firmware, Netapp H500e Firmware, Netapp H500s Firmware, Netapp H700e Firmware, Netapp H700s Firmware.

## How do I fix CVE-2021-3640?

Apply the vendor's patch.

## Is CVE-2021-3640 being exploited?

There is no known exploitation of CVE-2021-3640 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3640 and fix it if it is affected.

What it is: CVE-2021-3640 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 3 Mar 2022. 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-2021-3640 in the wild and no public exploit code.

Affected product: Canonical Ubuntu 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-2021-3640/ (Markdown: https://insights.sbomify.com/CVE-2021-3640/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3640
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3640
- OSV: https://osv.dev/vulnerability/CVE-2021-3640

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3640/
Summaries are generated and may contain mistakes; the official description above is the record.