# CVE-2021-3163: Cross-site Scripting in quill

> An attacker can execute arbitrary JavaScript via stored XSS in the Quill HTML editor, though researchers dispute this as intended browser behavior.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 12 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4943-9vgg-gr5r

## What is CVE-2021-3163?

CVE-2021-3163 is a medium-severity cross-site scripting vulnerability in n/a, published on 12 Apr 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

A vulnerability in the HTML editor of Slab Quill 4.8.0 allows an attacker to execute arbitrary JavaScript by storing an XSS payload (a crafted onloadstart attribute of an IMG element) in a text field. Note: Researchers have claimed that this issue is not within the product itself, but is intended behavior in a web browser

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

## Which versions are affected by CVE-2021-3163?

2 open source packages ship an affected version, including quill. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `quill` | npm | All versions to 1.3.7 | None |
| `quill` | npm | All versions to 1.3.7 | None |

Products: Slab Quill.

## How do I fix CVE-2021-3163?

No fix has been published for CVE-2021-3163 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3163 being exploited?

There is no known exploitation of CVE-2021-3163 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2025-15056](https://insights.sbomify.com/CVE-2025-15056/): Quill 2.0.3 - Lack of data validation in HTML export allowing XSS (medium 5.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3163 and fix it if it is affected.

What it is: CVE-2021-3163 is a medium-severity cross-site scripting vulnerability in n/a, published on 12 Apr 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-3163 in the wild and no public exploit code.

Affected packages and fixed versions:
- quill (npm): affected all versions up to 1.3.7; no fix listed
- quill (npm): affected all versions up to 1.3.7; no fix listed

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-2021-3163/ (Markdown: https://insights.sbomify.com/CVE-2021-3163/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3163
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3163
- OSV: https://osv.dev/vulnerability/CVE-2021-3163

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3163/
Summaries are generated and may contain mistakes; the official description above is the record.