# CVE-2021-40542: Cross-site scripting in n/a

> An unauthenticated attacker can inject and execute JavaScript code via the link_url parameter in Ajax_url_encode.php.

- **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:** 11 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-88f6-r22m-fxmf

## What is CVE-2021-40542?

CVE-2021-40542 is a medium-severity cross-site scripting vulnerability in Os4ed Opensis, published on 11 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

Opensis-Classic Version 8.0 is affected by cross-site scripting (XSS). An unauthenticated user can inject and execute JavaScript code through the link_url parameter in Ajax_url_encode.php.

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

## Which versions are affected by CVE-2021-40542?

It affects 1 product.


Products: Os4ed Opensis.

## How do I fix CVE-2021-40542?

No fix has been published for CVE-2021-40542 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40542 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-40542 exists.

Public exploit code:

- Opensis-Classic 8.0 - Cross-Site Scripting (nuclei): http/cves/2021/CVE-2021-40542.yaml

## Other vulnerabilities in Os4ed Opensis

- [CVE-2020-6143](https://insights.sbomify.com/CVE-2020-6143/): Code injection in OS4Ed (critical 10.0)
- [CVE-2020-6144](https://insights.sbomify.com/CVE-2020-6144/): Code injection in OS4Ed (critical 10.0)
- [CVE-2020-6142](https://insights.sbomify.com/CVE-2020-6142/): Path traversal in OS4Ed (critical 9.9)
- [CVE-2021-41691](https://insights.sbomify.com/CVE-2021-41691/): SQL injection in n/a (critical 9.8)
- [CVE-2025-22926](https://insights.sbomify.com/CVE-2025-22926/): Path traversal in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40542 and fix it if it is affected.

What it is: CVE-2021-40542 is a medium-severity cross-site scripting vulnerability in Os4ed Opensis, published on 11 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-40542 exists.

Affected product: Os4ed Opensis. 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-2021-40542/ (Markdown: https://insights.sbomify.com/CVE-2021-40542/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40542
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40542
- OSV: https://osv.dev/vulnerability/CVE-2021-40542

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40542/
Summaries are generated and may contain mistakes; the official description above is the record.