# CVE-2021-21799: Cross-site scripting in Advantech

> Cross-site scripting in Advantech R-SeeNet allows attackers to execute arbitrary JavaScript in a victim's browser via a crafted URL.

- **Severity:** Critical 9.6 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`)
- **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:** 16 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4jqw-vm5q-2f6h

## What is CVE-2021-21799?

CVE-2021-21799 is a critical cross-site scripting vulnerability in Advantech, published on 16 Jul 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

Cross-site scripting vulnerabilities exist in the telnet_form.php script functionality of Advantech R-SeeNet v 2.4.12 (20.10.2020). If a user visits a specially crafted URL, it can lead to arbitrary JavaScript code execution in the context of the targeted user’s browser. An attacker can provide a crafted URL to trigger this vulnerability.

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

## Which versions are affected by CVE-2021-21799?

It affects 1 product.


Products: Advantech R-Seenet.

## How do I fix CVE-2021-21799?

No fix has been published for CVE-2021-21799 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21799 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-21799 exists.

Public exploit code:

- Advantech R-SeeNet 2.4.12 - Cross-Site Scripting (nuclei): http/cves/2021/CVE-2021-21799.yaml

## Other vulnerabilities in Advantech

- [CVE-2023-5642](https://insights.sbomify.com/CVE-2023-5642/): Advantech R-SeeNet Unauthenticated Read/Write (critical 9.8)
- [CVE-2023-2611](https://insights.sbomify.com/CVE-2023-2611/): Advantech R-SeeNet Use of Hard-coded Credentials (critical 9.8)
- [CVE-2022-3385](https://insights.sbomify.com/CVE-2022-3385/): Memory corruption in R-SeeNet (critical 9.8)
- [CVE-2022-3386](https://insights.sbomify.com/CVE-2022-3386/): Memory corruption in R-SeeNet (critical 9.8)
- [CVE-2021-21805](https://insights.sbomify.com/CVE-2021-21805/): Command injection in Advantech (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21799 and fix it if it is affected.

What it is: CVE-2021-21799 is a critical cross-site scripting vulnerability in Advantech, published on 16 Jul 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-2021-21799 exists.

Affected product: Advantech. 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-2021-21799/ (Markdown: https://insights.sbomify.com/CVE-2021-21799/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21799
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21799
- OSV: https://osv.dev/vulnerability/CVE-2021-21799

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21799/
Summaries are generated and may contain mistakes; the official description above is the record.