# CVE-2021-4296: w3c Unicorn ValidatorNuMessage.java ValidatorNuMessage cross site scripting

> Remote attackers can inject malicious scripts via the ValidatorNuMessage function in W3C Unicorn, potentially executing code in user browsers.

- **Severity:** Low 3.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/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:** 29 Dec 2022
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-9cgm-gf5x-jx5x

## What is CVE-2021-4296?

CVE-2021-4296 is a low-severity cross-site scripting vulnerability in w3c Unicorn, published on 29 Dec 2022. 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 vulnerability, which was classified as problematic, has been found in w3c Unicorn. This issue affects the function ValidatorNuMessage of the file src/org/w3c/unicorn/response/impl/ValidatorNuMessage.java. The manipulation of the argument message leads to cross site scripting. The attack may be initiated remotely. The name of the patch is 51f75c31f7fc33859a9a571311c67ae4e95d9c68. It is recommended to apply a patch to fix this issue. The associated identifier of this vulnerability is VDB-217019.

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

## Which versions are affected by CVE-2021-4296?

It affects 1 product.


Products: W3 Unicorn.

## How do I fix CVE-2021-4296?

No fix has been published for CVE-2021-4296 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-4296 being exploited?

There is no known exploitation of CVE-2021-4296 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4296 and fix it if it is affected.

What it is: CVE-2021-4296 is a low-severity cross-site scripting vulnerability in w3c Unicorn, published on 29 Dec 2022. 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-2021-4296 in the wild and no public exploit code.

Affected product: w3c Unicorn. 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-2021-4296/ (Markdown: https://insights.sbomify.com/CVE-2021-4296/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4296
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4296
- OSV: https://osv.dev/vulnerability/CVE-2021-4296

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4296/
Summaries are generated and may contain mistakes; the official description above is the record.