CVE-2025-15056: Quill HTML Export XSS Vulnerability

CVE-2025-15056 Overview

A Cross-Site Scripting (XSS) vulnerability exists in the HTML export feature of Quill, a popular modern WYSIWYG editor. The vulnerability stems from a lack of data validation when exporting content to HTML format, allowing attackers to inject malicious scripts that execute in the context of a victim's browser session.

Critical Impact

Attackers can exploit this XSS vulnerability to execute arbitrary JavaScript code in the browsers of users viewing exported HTML content, potentially leading to session hijacking, credential theft, or malicious content injection.

Affected Products

• Quill version 2.0.3

Discovery Timeline

• 2026-01-13 - CVE CVE-2025-15056 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-15056

Vulnerability Analysis

This vulnerability is classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), commonly referred to as an injection vulnerability. The flaw exists within Quill's HTML export functionality, where user-supplied content is not properly validated or sanitized before being rendered as HTML output.

When a user creates content within the Quill editor and exports it to HTML format, the export mechanism fails to adequately escape or filter special characters and HTML entities. This allows an attacker to craft malicious input containing JavaScript payloads that persist through the export process and execute when the exported HTML is subsequently rendered in a browser.

The network-based attack vector means exploitation can occur remotely, though successful exploitation requires user interaction—specifically, a victim must view or open the malicious exported HTML content.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in Quill's HTML export feature. The export functionality does not properly sanitize user-controlled data before incorporating it into the generated HTML output, allowing script injection through specially crafted content. This represents a fundamental failure in the principle of treating all user input as untrusted and ensuring proper context-aware encoding of output.

Attack Vector

The attack leverages the network-accessible nature of web applications using Quill. An attacker can exploit this vulnerability through the following general flow:

1. The attacker crafts malicious content containing JavaScript payloads within the Quill editor
2. The content is exported using the HTML export feature, which fails to sanitize the malicious payload
3. The exported HTML containing the XSS payload is shared or made accessible to potential victims
4. When victims view the exported HTML content, the malicious JavaScript executes in their browser context

This attack requires user interaction as victims must access the compromised HTML content. The impact affects the integrity of downstream systems that consume the exported content, potentially enabling session hijacking, phishing attacks, or malware distribution.

For detailed technical analysis and proof of concept information, refer to the Fluid Attacks Security Advisory.

Detection Methods for CVE-2025-15056

Indicators of Compromise

• Unexpected JavaScript code appearing in HTML exports from Quill-based applications
• Anomalous script tags or event handler attributes in exported content
• User reports of suspicious browser behavior when viewing exported HTML documents
• Web application firewall alerts indicating XSS payload patterns in Quill editor submissions

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block inline script execution
• Deploy web application firewalls configured to identify common XSS payload patterns in user submissions
• Enable logging and monitoring of Quill editor submissions for suspicious content patterns
• Use browser developer tools to inspect exported HTML for unexpected script elements

Monitoring Recommendations

• Monitor application logs for patterns indicative of XSS injection attempts
• Set up alerts for Content Security Policy violation reports
• Track and audit exported HTML content for anomalous script inclusions
• Implement real-time scanning of user-generated content before export

How to Mitigate CVE-2025-15056

Immediate Actions Required

• Audit all applications using Quill version 2.0.3 to assess exposure
• Implement server-side HTML sanitization for all exported content as an additional defense layer
• Deploy Content Security Policy headers to mitigate the impact of potential XSS exploitation
• Consider temporarily disabling the HTML export feature in critical applications until a patch is available

Patch Information

At the time of publication, organizations should monitor the Quill GitHub repository for security updates and patches addressing this vulnerability. Review vendor release notes and security advisories for specific patch information when available.

Workarounds

• Implement server-side HTML sanitization using established libraries (e.g., DOMPurify) to filter exported content before distribution
• Apply strict Content Security Policy headers to prevent execution of inline scripts
• Validate and sanitize all user input before it enters the Quill editor
• Consider using an allow-list approach for HTML elements and attributes in exported content

# Example CSP header configuration to mitigate XSS impact
# Add to web server configuration (Apache example)
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"

# Nginx example
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'";