# CVE-2021-42567: Cross-site Scripting in Apereo CAS

> Cross-site scripting in Apereo CAS REST API allows attackers to execute scripts in user sessions, potentially leading to 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:** Yes
- **Published:** 7 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-gfhx-jjwq-63gv

## What is CVE-2021-42567?

CVE-2021-42567 is a medium-severity cross-site scripting vulnerability in n/a, published on 7 Dec 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

Apereo CAS through 6.4.1 allows XSS via POST requests sent to the REST API endpoints.

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

## Which versions are affected by CVE-2021-42567?

2 open source packages ship an affected version, including org.apereo.cas:cas-server-core-web. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `org.apereo.cas:cas-server-core-web` | Maven | All versions | 6.4.2 |
| `org.apereo.cas:cas-server-core-web` | Maven | All versions | 6.4.2 |

Products: Apereo Central Authentication Service.

## How do I fix CVE-2021-42567?

Upgrade org.apereo.cas:cas-server-core-web to 6.4.2 or later.

## Is CVE-2021-42567 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-42567 exists.

Public exploit code:

- Apereo CAS Cross-Site Scripting (nuclei): http/cves/2021/CVE-2021-42567.yaml

## Other vulnerabilities in n/a

- [CVE-2023-4612](https://insights.sbomify.com/CVE-2023-4612/): MFA bypass in Apereo CAS (critical 9.8)
- [CVE-2024-4399](https://insights.sbomify.com/CVE-2024-4399/): CAS <= 1.0.0 - Unauthenticated SSRF (critical 9.1)
- [CVE-2019-10754](https://insights.sbomify.com/CVE-2019-10754/): Use of Insufficiently Random Values in Apereo CAS (high 8.1)
- [CVE-2020-27178](https://insights.sbomify.com/CVE-2020-27178/): Improper Authentication in Apereo CAS (high 7.5)
- [CVE-2015-1169](https://insights.sbomify.com/CVE-2015-1169/): Auth bypass in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-42567 and fix it if it is affected.

What it is: CVE-2021-42567 is a medium-severity cross-site scripting vulnerability in n/a, published on 7 Dec 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-42567 exists.

Affected packages and fixed versions:
- org.apereo.cas:cas-server-core-web (Maven): affected all versions; fixed in 6.4.2
- org.apereo.cas:cas-server-core-web (Maven): affected all versions; fixed in 6.4.2

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-2021-42567/ (Markdown: https://insights.sbomify.com/CVE-2021-42567/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-42567
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-42567
- OSV: https://osv.dev/vulnerability/CVE-2021-42567

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-42567/
Summaries are generated and may contain mistakes; the official description above is the record.