# CVE-2021-28931: Arbitrary file upload in Fork CMS

> Attackers can upload malicious zip files to the Themes panel to create or replace arbitrary files, potentially leading to code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-748f-wv76-x9hg

## What is CVE-2021-28931?

CVE-2021-28931 is a high-severity vulnerability in n/a, published on 7 Jul 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Arbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to create or replace arbitrary files in the /themes directory via a crafted zip file uploaded to the Themes panel.

Weakness: CWE-434 (Unrestricted Upload of File with Dangerous Type)

## Which versions are affected by CVE-2021-28931?

2 open source packages ship an affected version, including forkcms/forkcms. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `forkcms/forkcms` | Packagist | All versions | 5.9.3 |
| `forkcms/forkcms` | Packagist | All versions | 5.9.3 |

Products: Fork-Cms Fork Cms.

## How do I fix CVE-2021-28931?

Upgrade forkcms/forkcms to 5.9.3 or later.

## Is CVE-2021-28931 being exploited?

There is no known exploitation of CVE-2021-28931 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2019-15521](https://insights.sbomify.com/CVE-2019-15521/): Spoon Library as used in Fork CMS allows PHP object injection (critical 9.8)
- [CVE-2022-0153](https://insights.sbomify.com/CVE-2022-0153/): SQL Injection in forkcms/forkcms (critical 9.6)
- [CVE-2022-1064](https://insights.sbomify.com/CVE-2022-1064/): SQL injection through marking blog comments on bulk as spam in forkcms/forkcms (critical 9.0)
- [CVE-2020-23264](https://insights.sbomify.com/CVE-2020-23264/): Cross-Site Request Forgery in forkcms (high 8.8)
- [CVE-2020-24036](https://insights.sbomify.com/CVE-2020-24036/): Deserialization in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28931 and fix it if it is affected.

What it is: CVE-2021-28931 is a high-severity vulnerability in n/a, published on 7 Jul 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-2021-28931 in the wild and no public exploit code.

Affected packages and fixed versions:
- forkcms/forkcms (Packagist): affected all versions; fixed in 5.9.3
- forkcms/forkcms (Packagist): affected all versions; fixed in 5.9.3

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-2021-28931/ (Markdown: https://insights.sbomify.com/CVE-2021-28931/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28931
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28931
- OSV: https://osv.dev/vulnerability/CVE-2021-28931

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28931/
Summaries are generated and may contain mistakes; the official description above is the record.