# CVE-2020-21387: Cross-site scripting in n/a

> Attackers can steal administrator cookies via XSS in Maccms, leading to privilege escalation and account takeover.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 4 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-h27q-vg4q-q84x

## What is CVE-2020-21387?

CVE-2020-21387 is a medium-severity cross-site scripting vulnerability in n/a, published on 4 Oct 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

A cross-site scripting (XSS) vulnerability in the parameter type_en of Maccms 10 allows attackers to obtain the administrator cookie and escalate privileges via a crafted payload.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2020-21387?

It affects 1 product.


Products: Maccms Maccms.

## How do I fix CVE-2020-21387?

No fix has been published for CVE-2020-21387 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-21387 being exploited?

There is no known exploitation of CVE-2020-21387 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-45786](https://insights.sbomify.com/CVE-2021-45786/): Auth bypass in n/a (critical 9.8)
- [CVE-2020-21359](https://insights.sbomify.com/CVE-2020-21359/): File upload in n/a (critical 9.8)
- [CVE-2017-17733](https://insights.sbomify.com/CVE-2017-17733/): Command injection in n/a (critical 9.8)
- [CVE-2025-28089](https://insights.sbomify.com/CVE-2025-28089/): Server-side request forgery in n/a (critical 9.1)
- [CVE-2025-28090](https://insights.sbomify.com/CVE-2025-28090/): Server-side request forgery in n/a (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-21387 and fix it if it is affected.

What it is: CVE-2020-21387 is a medium-severity cross-site scripting vulnerability in n/a, published on 4 Oct 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-21387 in the wild and no public exploit code.

Affected product: n/a. 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-2020-21387/ (Markdown: https://insights.sbomify.com/CVE-2020-21387/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-21387
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-21387
- OSV: https://osv.dev/vulnerability/CVE-2020-21387

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-21387/
Summaries are generated and may contain mistakes; the official description above is the record.