# CVE-2020-8831: World writable root owned lock file created in user controllable location

> An attacker can exploit a symlink vulnerability in Apport's lock file creation to escalate privileges on Ubuntu systems.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N`)
- **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:** 22 Apr 2020
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-33w2-prhc-2q89, UBUNTU-CVE-2020-8831

## What is CVE-2020-8831?

CVE-2020-8831 is a medium-severity path traversal vulnerability in Canonical Ubuntu Linux, published on 22 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Apport creates a world writable lock file with root ownership in the world writable /var/lock/apport directory. If the apport/ directory does not exist (this is not uncommon as /var/lock is a tmpfs), it will create the directory, otherwise it will simply continue execution using the existing directory. This allows for a symlink attack if an attacker were to create a symlink at /var/lock/apport, changing apport's lock file location. This file could then be used to escalate privileges, for example. Fixed in versions 2.20.1-0ubuntu2.23, 2.20.9-0ubuntu7.14, 2.20.11-0ubuntu8.8 and 2.20.11-0ubuntu22.

Weakness: CWE-59 (Improper Link Resolution Before File Access), CWE-379 (Creation of Temporary File in Directory with Insecure Permissions)

## Which versions are affected by CVE-2020-8831?

It affects 2 products.


Products: Apport Project Apport, Canonical Ubuntu Linux.

## How do I fix CVE-2020-8831?

Apply the vendor's patch.

## Is CVE-2020-8831 being exploited?

There is no known exploitation of CVE-2020-8831 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2022-28657](https://insights.sbomify.com/CVE-2022-28657/): Denial of service in Apport (high 7.8)
- [CVE-2018-6552](https://insights.sbomify.com/CVE-2018-6552/): Apport treats the container PID as the global PID when /proc/<global_pid>/ is missing (high 7.8)
- [CVE-2017-14177](https://insights.sbomify.com/CVE-2017-14177/): Privilege escalation in Apport (high 7.8)
- [CVE-2017-14179](https://insights.sbomify.com/CVE-2017-14179/): Privilege escalation in Apport (high 7.8)
- [CVE-2017-14180](https://insights.sbomify.com/CVE-2017-14180/): Privilege escalation in Apport (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-8831 and fix it if it is affected.

What it is: CVE-2020-8831 is a medium-severity path traversal vulnerability in Canonical Ubuntu Linux, published on 22 Apr 2020. 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-2020-8831 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-2020-8831/ (Markdown: https://insights.sbomify.com/CVE-2020-8831/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-8831
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-8831
- OSV: https://osv.dev/vulnerability/CVE-2020-8831

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-8831/
Summaries are generated and may contain mistakes; the official description above is the record.