# CVE-2021-27821: Cross-site scripting in n/a

> An attacker can inject malicious scripts into the OpenWRT LuCI web interface, potentially compromising user sessions or data.

- **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:** 25 May 2021
- **Updated:** 9 Jul 2026
- **Also known as:** GHSA-4r8j-5v22-gg78

## What is CVE-2021-27821?

CVE-2021-27821 is a medium-severity cross-site scripting vulnerability in n/a, published on 25 May 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

The Web Interface for OpenWRT LuCI version 19.07 and lower has been discovered to have a cross-site scripting vulnerability.

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

## Which versions are affected by CVE-2021-27821?

It affects 1 product.


Products: Openwrt Luci.

## How do I fix CVE-2021-27821?

No fix has been published for CVE-2021-27821 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27821 being exploited?

There is no known exploitation of CVE-2021-27821 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2019-12272](https://insights.sbomify.com/CVE-2019-12272/): Command injection in n/a (critical 9.8)
- [CVE-2026-32721](https://insights.sbomify.com/CVE-2026-32721/): LuCI luci-mod-network: Possible XSS attack in WiFi scan on Joining Wireless Client modal (high 8.6)
- [CVE-2023-24181](https://insights.sbomify.com/CVE-2023-24181/): Cross-site scripting in n/a (medium 5.4)
- [CVE-2022-41435](https://insights.sbomify.com/CVE-2022-41435/): Cross-site scripting in n/a (medium 5.4)
- [CVE-2020-10871](https://insights.sbomify.com/CVE-2020-10871/): Information disclosure in n/a (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27821 and fix it if it is affected.

What it is: CVE-2021-27821 is a medium-severity cross-site scripting vulnerability in n/a, published on 25 May 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: There is no known exploitation of CVE-2021-27821 in the wild and no public exploit code.

Affected product: n/a. 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-2021-27821/ (Markdown: https://insights.sbomify.com/CVE-2021-27821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27821
- OSV: https://osv.dev/vulnerability/CVE-2021-27821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27821/
Summaries are generated and may contain mistakes; the official description above is the record.