# CVE-2021-20855: Cross-site scripting in ELECOM LAN routers

> Remote authenticated attackers can inject arbitrary scripts into ELECOM LAN routers, potentially compromising user sessions or device integrity.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/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:** 1 Dec 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-9cr9-j2r9-7m87

## What is CVE-2021-20855?

CVE-2021-20855 is a medium-severity cross-site scripting vulnerability in ELECOM LAN routers, published on 1 Dec 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

Cross-site scripting vulnerability in ELECOM LAN routers (WRH-733GBK firmware v1.02.9 and prior and WRH-733GWH firmware v1.02.9 and prior) allows a remote authenticated attacker to inject an arbitrary script via unspecified vectors.

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

## Which versions are affected by CVE-2021-20855?

It affects 2 products.


Products: Elecom Wrh-733gbk Firmware, Elecom Wrh-733gwh Firmware.

## How do I fix CVE-2021-20855?

No fix has been published for CVE-2021-20855 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20855 being exploited?

There is no known exploitation of CVE-2021-20855 in the wild and no public exploit code.

## Other vulnerabilities in ELECOM LAN routers

- [CVE-2021-20852](https://insights.sbomify.com/CVE-2021-20852/): Command injection in ELECOM LAN routers (medium 6.8)
- [CVE-2021-20853](https://insights.sbomify.com/CVE-2021-20853/): Command injection in ELECOM LAN routers (medium 6.8)
- [CVE-2021-20854](https://insights.sbomify.com/CVE-2021-20854/): Command injection in ELECOM LAN routers (medium 6.8)
- [CVE-2021-20856](https://insights.sbomify.com/CVE-2021-20856/): Cross-site scripting in ELECOM LAN routers (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20855 and fix it if it is affected.

What it is: CVE-2021-20855 is a medium-severity cross-site scripting vulnerability in ELECOM LAN routers, published on 1 Dec 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-2021-20855 in the wild and no public exploit code.

Affected product: ELECOM LAN routers. 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-2021-20855/ (Markdown: https://insights.sbomify.com/CVE-2021-20855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20855
- OSV: https://osv.dev/vulnerability/CVE-2021-20855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20855/
Summaries are generated and may contain mistakes; the official description above is the record.