# CVE-2021-26539: Improper Input Validation in sanitize-html

> An attacker can bypass iframe hostname whitelisting in sanitize-html by exploiting internationalized domain name handling flaws.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-rjqq-98f6-6j3r, ROOT-APP-NPM-CVE-2021-26539

## What is CVE-2021-26539?

CVE-2021-26539 is a medium-severity vulnerability in n/a, published on 8 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Apostrophe Technologies sanitize-html before 2.3.1 does not properly handle internationalized domain name (IDN) which could allow an attacker to bypass hostname whitelist validation set by the "allowedIframeHostnames" option.

## Which versions are affected by CVE-2021-26539?

2 open source packages ship an affected version, including sanitize-html. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `sanitize-html` | npm | All versions | 2.3.1 |
| `sanitize-html` | npm | All versions | 2.3.1 |

Products: Apostrophecms Sanitize-Html.

## How do I fix CVE-2021-26539?

Upgrade sanitize-html to 2.3.1 or later.

## Is CVE-2021-26539 being exploited?

There is no known exploitation of CVE-2021-26539 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2014-125128](https://insights.sbomify.com/CVE-2014-125128/): Cross-site scripting in apostrophecms:sanitize-html (medium 6.1)
- [CVE-2019-25225](https://insights.sbomify.com/CVE-2019-25225/): sanitize-html is vulnerable to XSS through incomprehensive sanitization (medium 6.1)
- [CVE-2016-1000237](https://insights.sbomify.com/CVE-2016-1000237/): Cross-Site Scripting in sanitize-html (medium 6.1)
- [CVE-2024-21501](https://insights.sbomify.com/CVE-2024-21501/): sanitize-html Information Exposure vulnerability (medium 5.3)
- [CVE-2022-25887](https://insights.sbomify.com/CVE-2022-25887/): Regular Expression Denial of Service (ReDoS) (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26539 and fix it if it is affected.

What it is: CVE-2021-26539 is a medium-severity vulnerability in n/a, published on 8 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-26539 in the wild and no public exploit code.

Affected packages and fixed versions:
- sanitize-html (npm): affected all versions; fixed in 2.3.1
- sanitize-html (npm): affected all versions; fixed in 2.3.1

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-2021-26539/ (Markdown: https://insights.sbomify.com/CVE-2021-26539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26539
- OSV: https://osv.dev/vulnerability/CVE-2021-26539

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26539/
Summaries are generated and may contain mistakes; the official description above is the record.