# CVE-2021-28806: DOM-Based XSS Vulnerability in QTS and QuTS hero

> Attackers can inject malicious scripts into QNAP NAS web interfaces, potentially leading to code execution or account takeover.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/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:** 3 Jun 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-q3xx-v678-8w29

## What is CVE-2021-28806?

CVE-2021-28806 is a medium-severity cross-site scripting vulnerability in Qnap Qts, published on 3 Jun 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

A DOM-based XSS vulnerability has been reported to affect QNAP NAS running QTS and QuTS hero. If exploited, this vulnerability allows attackers to inject malicious code. This issue affects: QNAP Systems Inc. QTS versions prior to 4.5.3.1652 Build 20210428. QNAP Systems Inc. QuTS hero versions prior to h4.5.2.1638 Build 20210414. QNAP Systems Inc. QuTScloud versions prior to c4.5.5.1656 Build 20210503. This issue does not affect: QNAP Systems Inc. QTS 4.3.6; 4.3.3.

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

## Which versions are affected by CVE-2021-28806?

It affects 3 products.


Products: Qnap Qts, Qnap Quts Hero, Qnap Qutscloud.

## How do I fix CVE-2021-28806?

No fix has been published for CVE-2021-28806 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-28806 being exploited?

There is no known exploitation of CVE-2021-28806 in the wild and no public exploit code.

## Other vulnerabilities in Qnap Qts

- [CVE-2020-2509](https://insights.sbomify.com/CVE-2020-2509/): QNAP Network-Attached Storage (NAS) Command Injection (critical 9.8, exploited in the wild)
- [CVE-2018-19949](https://insights.sbomify.com/CVE-2018-19949/): QNAP NAS File Station Command Injection (critical 9.8, exploited in the wild)
- [CVE-2019-7193](https://insights.sbomify.com/CVE-2019-7193/): QNAP QTS Improper Input Validation (critical 9.8, exploited in the wild)
- [CVE-2018-19943](https://insights.sbomify.com/CVE-2018-19943/): QNAP NAS File Station Cross-Site Scripting (high 8.0, exploited in the wild)
- [CVE-2018-19953](https://insights.sbomify.com/CVE-2018-19953/): QNAP NAS File Station Cross-Site Scripting (medium 6.1, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28806 and fix it if it is affected.

What it is: CVE-2021-28806 is a medium-severity cross-site scripting vulnerability in Qnap Qts, published on 3 Jun 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-2021-28806 in the wild and no public exploit code.

Affected product: Qnap Qts. 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-2021-28806/ (Markdown: https://insights.sbomify.com/CVE-2021-28806/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28806
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28806
- OSV: https://osv.dev/vulnerability/CVE-2021-28806

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28806/
Summaries are generated and may contain mistakes; the official description above is the record.