# CVE-2020-27837: Race condition in gdm

> A race condition in GDM allows bypassing the lock screen for users with autologin enabled, granting unauthorized session access.

- **Severity:** Medium 6.4 (`CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-27837, GHSA-xpm4-75c2-wrgc, OESA-2022-1811, OESA-2022-1812, UBUNTU-CVE-2020-27837

## What is CVE-2020-27837?

CVE-2020-27837 is a medium-severity vulnerability in gdm, published on 28 Dec 2020. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in GDM in versions prior to 3.38.2.1. A race condition in the handling of session shutdown makes it possible to bypass the lock screen for a user that has autologin enabled, accessing their session without authentication. This is similar to CVE-2017-12164, but requires more difficult conditions to exploit.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2020-27837?

It affects 1 product.


Products: Gnome Gnome Display Manager.

## How do I fix CVE-2020-27837?

Upgrade to a fixed version.

## Is CVE-2020-27837 being exploited?

There is no known exploitation of CVE-2020-27837 in the wild and no public exploit code.

## Other vulnerabilities in gdm

- [CVE-2018-14424](https://insights.sbomify.com/CVE-2018-14424/): Use after free in n/a (high 7.8)
- [CVE-2020-16125](https://insights.sbomify.com/CVE-2020-16125/): gdm3 would start gnome-initial-setup if it cannot contact accountservice (high 7.2)
- [CVE-2013-4169](https://insights.sbomify.com/CVE-2013-4169/): Path traversal in n/a (medium 6.9)
- [CVE-2017-12164](https://insights.sbomify.com/CVE-2017-12164/): Auth bypass in gdm (medium 4.1)
- [CVE-2013-7273](https://insights.sbomify.com/CVE-2013-7273/): Denial of service in n/a (low 2.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27837 and fix it if it is affected.

What it is: CVE-2020-27837 is a medium-severity vulnerability in gdm, published on 28 Dec 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-2020-27837 in the wild and no public exploit code.

Affected product: gdm. 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-2020-27837/ (Markdown: https://insights.sbomify.com/CVE-2020-27837/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27837
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27837
- OSV: https://osv.dev/vulnerability/CVE-2020-27837

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From sbomify Insights: https://insights.sbomify.com/CVE-2020-27837/
Summaries are generated and may contain mistakes; the official description above is the record.