# CVE-2020-26239: Cross-Site Scripting in Scratch browser addons

> A DOM-based XSS vulnerability in the Scratch Addons browser extension allows attackers to execute arbitrary scripts when a victim visits a malicious website.

- **Severity:** High 7.6 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/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:** 23 Nov 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-6qfq-px3r-xj4p

## What is CVE-2020-26239?

CVE-2020-26239 is a high-severity cross-site scripting vulnerability in ScratchAddons, published on 23 Nov 2020. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Scratch Addons is a WebExtension that supports both Chrome and Firefox. Scratch Addons before version 1.3.2 is vulnerable to DOM-based XSS. If the victim visited a specific website, the More Links addon of the Scratch Addons extension used incorrect regular expression which caused the HTML-escaped values to be unescaped, leading to XSS. Scratch Addons version 1.3.2 fixes the bug. The extension will be automatically updated by the browser. More Links addon can be disabled via the option of the extension.

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

## Which versions are affected by CVE-2020-26239?

It affects 1 product.


Products: Scratchaddons Scratch Addons.

## How do I fix CVE-2020-26239?

No fix has been published for CVE-2020-26239 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-26239 being exploited?

There is no known exploitation of CVE-2020-26239 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26239 and fix it if it is affected.

What it is: CVE-2020-26239 is a high-severity cross-site scripting vulnerability in ScratchAddons, published on 23 Nov 2020. 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-2020-26239 in the wild and no public exploit code.

Affected product: ScratchAddons. 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-2020-26239/ (Markdown: https://insights.sbomify.com/CVE-2020-26239/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26239
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26239
- OSV: https://osv.dev/vulnerability/CVE-2020-26239

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-26239/
Summaries are generated and may contain mistakes; the official description above is the record.