# CVE-2020-16127: accountsservice .pam_environment infinite loop

> An attacker can cause a denial of service by symlinking /dev/zero to ~/.pam_environment, triggering an infinite loop in AccountsService.

- **Severity:** Low 2.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 11 Nov 2020
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-vg2p-x98m-7mxr, UBUNTU-CVE-2020-16127

## What is CVE-2020-16127?

CVE-2020-16127 is a low-severity denial of service vulnerability in Freedesktop accountsservice, published on 11 Nov 2020. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

An Ubuntu-specific modification to AccountsService in versions before 0.6.55-0ubuntu13.2, among other earlier versions, would perform unbounded read operations on user-controlled ~/.pam_environment files, allowing an infinite loop if /dev/zero is symlinked to this location.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2020-16127?

It affects 1 product.


Products: Freedesktop Accountsservice.

## How do I fix CVE-2020-16127?

Apply the vendor's patch.

## Is CVE-2020-16127 being exploited?

There is no known exploitation of CVE-2020-16127 in the wild and no public exploit code.

## Other vulnerabilities in Freedesktop accountsservice

- [CVE-2018-14036](https://insights.sbomify.com/CVE-2018-14036/): Path traversal in n/a (medium 6.5)
- [CVE-2020-16126](https://insights.sbomify.com/CVE-2020-16126/): accountsservice drops ruid, allows unprivileged users to send it signals (low 3.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-16127 and fix it if it is affected.

What it is: CVE-2020-16127 is a low-severity denial of service vulnerability in Freedesktop accountsservice, published on 11 Nov 2020. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-16127 in the wild and no public exploit code.

Affected product: Freedesktop accountsservice. 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-2020-16127/ (Markdown: https://insights.sbomify.com/CVE-2020-16127/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-16127
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-16127
- OSV: https://osv.dev/vulnerability/CVE-2020-16127

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-16127/
Summaries are generated and may contain mistakes; the official description above is the record.