# CVE-2021-40100: Cross-site scripting in n/a

> Attackers can inject malicious scripts into Concrete CMS conversations when the Rich Text editor is enabled, potentially compromising user sessions.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 24 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-mqg6-3r82-f53h

## What is CVE-2021-40100?

CVE-2021-40100 is a medium-severity cross-site scripting vulnerability in Concretecms Concrete Cms, published on 24 Sep 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

An issue was discovered in Concrete CMS through 8.5.5. Stored XSS can occur in Conversations when the Active Conversation Editor is set to Rich Text.

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

## Which versions are affected by CVE-2021-40100?

It affects 1 product.


Products: Concretecms Concrete Cms.

## How do I fix CVE-2021-40100?

No fix has been published for CVE-2021-40100 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40100 being exploited?

There is no known exploitation of CVE-2021-40100 in the wild and no public exploit code.

## Other vulnerabilities in Concretecms Concrete Cms

- [CVE-2023-48648](https://insights.sbomify.com/CVE-2023-48648/): Concrete CMS allows unauthorized access because directories can be created with insecure permissions (critical 9.8)
- [CVE-2022-21829](https://insights.sbomify.com/CVE-2022-21829/): Code injection in concrete CMS (critical 9.8)
- [CVE-2021-22958](https://insights.sbomify.com/CVE-2021-22958/): Server-Side Request Forgery vulnerability in concrete5 (critical 9.8)
- [CVE-2021-40098](https://insights.sbomify.com/CVE-2021-40098/): Path traversal in n/a (critical 9.8)
- [CVE-2026-8134](https://insights.sbomify.com/CVE-2026-8134/): Concrete CMS Vulnerable to Relative Path Traversal (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40100 and fix it if it is affected.

What it is: CVE-2021-40100 is a medium-severity cross-site scripting vulnerability in Concretecms Concrete Cms, published on 24 Sep 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-40100 in the wild and no public exploit code.

Affected product: Concretecms Concrete Cms. 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-2021-40100/ (Markdown: https://insights.sbomify.com/CVE-2021-40100/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40100
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40100
- OSV: https://osv.dev/vulnerability/CVE-2021-40100

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40100/
Summaries are generated and may contain mistakes; the official description above is the record.