# CVE-2021-20866: Missing authorization in Advanced Custom Fields and Advanced Custom Fields Pro

> An attacker can obtain unauthorized user list information due to missing authorization checks in the Advanced Custom Fields plugin.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Dec 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-gcpg-c569-xfr4

## What is CVE-2021-20866?

CVE-2021-20866 is a medium-severity missing authorization vulnerability in Delicious Brains Advanced Custom Fields and Advanced Custom Fields Pro, published on 13 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing authorization vulnerability in obtaining the user list which may allow a user to obtain the unauthorized information via unspecified vectors.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2021-20866?

It affects 1 product.


Products: Advancedcustomfields Advanced Custom Fields.

## How do I fix CVE-2021-20866?

No fix has been published for CVE-2021-20866 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20866 being exploited?

There is no known exploitation of CVE-2021-20866 in the wild and no public exploit code.

## Other vulnerabilities in Delicious Brains Advanced Custom Fields and Advanced Custom Fields Pro

- [CVE-2023-1196](https://insights.sbomify.com/CVE-2023-1196/): Advanced Custom Fields - Contributor+ PHP Object Injection (high 8.8)
- [CVE-2022-2594](https://insights.sbomify.com/CVE-2022-2594/): Advanced Custom Fields 5.0-5.12.2 - Unauthenticated File Upload (high 8.8)
- [CVE-2024-4565](https://insights.sbomify.com/CVE-2024-4565/): Advanced Custom Fields < 6.3 - Contributor+ Custom Field Access (high 7.5)
- [CVE-2021-20865](https://insights.sbomify.com/CVE-2021-20865/): Missing authorization in Advanced Custom Fields and Advanced Custom Fields Pro (high 7.5)
- [CVE-2023-30777](https://insights.sbomify.com/CVE-2023-30777/): WordPress Advanced Custom Fields / Advanced Custom Fields PRO plugins <= 6.1.5 vulnerable to Cross Site Scripting (XSS) (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20866 and fix it if it is affected.

What it is: CVE-2021-20866 is a medium-severity missing authorization vulnerability in Delicious Brains Advanced Custom Fields and Advanced Custom Fields Pro, published on 13 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-20866 in the wild and no public exploit code.

Affected product: Delicious Brains Advanced Custom Fields and Advanced Custom Fields Pro. 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-2021-20866/ (Markdown: https://insights.sbomify.com/CVE-2021-20866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20866
- OSV: https://osv.dev/vulnerability/CVE-2021-20866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20866/
Summaries are generated and may contain mistakes; the official description above is the record.