# CVE-2021-3831: Cross-site Scripting (XSS) - Reflected in gnuboard/gnuboard5

> Attackers can inject malicious scripts into gnuboard5 pages, potentially stealing user data or hijacking sessions.

- **Severity:** High 7.1 (`CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Dec 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-xq54-j4gh-pm4j

## What is CVE-2021-3831?

CVE-2021-3831 is a high-severity cross-site scripting vulnerability in gnuboard/gnuboard5, published on 14 Dec 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

gnuboard5 is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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

## Which versions are affected by CVE-2021-3831?

It affects 1 product.


Products: Gnuboard Gnuboard5.

## How do I fix CVE-2021-3831?

No fix has been published for CVE-2021-3831 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3831 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-3831 exists.

Public exploit code:

- Unauthenticated Sensitive Information Disclosure (github_poc): https://github.com/aratane/CVE-2021-3831
- Gnuboard 5 - Cross-Site Scripting (nuclei): http/cves/2021/CVE-2021-3831.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3831 and fix it if it is affected.

What it is: CVE-2021-3831 is a high-severity cross-site scripting vulnerability in gnuboard/gnuboard5, published on 14 Dec 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-3831 exists.

Affected product: gnuboard/gnuboard5. 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-2021-3831/ (Markdown: https://insights.sbomify.com/CVE-2021-3831/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3831
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3831
- OSV: https://osv.dev/vulnerability/CVE-2021-3831

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3831/
Summaries are generated and may contain mistakes; the official description above is the record.