# CVE-2021-24153: Yoast SEO < 3.4.1 - Authenticated Stored Cross-Site Scripting (XSS)

> Authenticated attackers can inject malicious scripts via bypassed blacklist filters in the Yoast SEO plugin, potentially compromising user sessions.

- **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:** 5 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-qj4c-xvxc-5hqj

## What is CVE-2021-24153?

CVE-2021-24153 is a medium-severity cross-site scripting vulnerability in Unknown Yoast SEO, published on 5 Apr 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 Stored Cross-Site Scripting vulnerability was discovered in the Yoast SEO WordPress plugin before 3.4.1, which had built-in blacklist filters which were blacklisting Parenthesis as well as several functions such as alert but bypasses were found.

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

## Which versions are affected by CVE-2021-24153?

It affects 1 product.


Products: Yoast Yoast Seo.

## How do I fix CVE-2021-24153?

No fix has been published for CVE-2021-24153 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-24153 being exploited?

There is no known exploitation of CVE-2021-24153 in the wild and no public exploit code.

## Other vulnerabilities in Unknown Yoast SEO

- [CVE-2019-13478](https://insights.sbomify.com/CVE-2019-13478/): Cross-site scripting in n/a (critical 9.9)
- [CVE-2023-32300](https://insights.sbomify.com/CVE-2023-32300/): WordPress Yoast SEO: Local Plugin <= 14.8 is vulnerable to Cross Site Scripting (XSS) (high 7.1)
- [CVE-2018-19370](https://insights.sbomify.com/CVE-2018-19370/): Race condition in n/a (medium 6.6)
- [CVE-2023-28785](https://insights.sbomify.com/CVE-2023-28785/): WordPress Yoast SEO: Local Plugin <= 14.9 is vulnerable to Cross Site Scripting (XSS) (medium 6.5)
- [CVE-2021-31779](https://insights.sbomify.com/CVE-2021-31779/): Server-Side Request Forgery in yoast_seo (medium 6.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-24153 and fix it if it is affected.

What it is: CVE-2021-24153 is a medium-severity cross-site scripting vulnerability in Unknown Yoast SEO, published on 5 Apr 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-2021-24153 in the wild and no public exploit code.

Affected product: Unknown Yoast SEO. 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-2021-24153/ (Markdown: https://insights.sbomify.com/CVE-2021-24153/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-24153
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-24153
- OSV: https://osv.dev/vulnerability/CVE-2021-24153

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-24153/
Summaries are generated and may contain mistakes; the official description above is the record.