# CVE-2021-3899: Race condition in Apport

> A race condition in Apport allows local attackers to execute arbitrary code as root under specific configurations.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/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 Jun 2024
- **Updated:** 19 Aug 2024
- **Also known as:** GHSA-m676-gr96-hhhh, UBUNTU-CVE-2021-3899

## What is CVE-2021-3899?

CVE-2021-3899 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 3 Jun 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

There is a race condition in the 'replaced executable' detection that, with the correct local configuration, allow an attacker to execute arbitrary code as root.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2021-3899?

It affects 2 products.


Products: Canonical Apport, Canonical Ubuntu Linux.

## How do I fix CVE-2021-3899?

Apply the vendor's patch.

## Is CVE-2021-3899 being exploited?

There is no known exploitation of CVE-2021-3899 in the wild and no public exploit code.

Public exploit code:

- race condition in apport lead to Local Privilege Escalation on Ubuntu (github_poc): https://github.com/liumuqing/CVE-2021-3899_PoC

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2021-25682](https://insights.sbomify.com/CVE-2021-25682/): apport improperly parses /proc/pid/status (high 8.8)
- [CVE-2021-25683](https://insights.sbomify.com/CVE-2021-25683/): apport improperly parses /proc/pid/stat (high 8.8)
- [CVE-2021-25684](https://insights.sbomify.com/CVE-2021-25684/): apport can be stalled by reading a FIFO (high 8.8)
- [CVE-2022-1242](https://insights.sbomify.com/CVE-2022-1242/): Other in Apport (high 7.8)
- [CVE-2023-1326](https://insights.sbomify.com/CVE-2023-1326/): local privilege escalation in apport-cli (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3899 and fix it if it is affected.

What it is: CVE-2021-3899 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 3 Jun 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-2021-3899 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-2021-3899/ (Markdown: https://insights.sbomify.com/CVE-2021-3899/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3899
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3899
- OSV: https://osv.dev/vulnerability/CVE-2021-3899

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3899/
Summaries are generated and may contain mistakes; the official description above is the record.