CVE-2025-15056 Overview
CVE-2025-15056 is a Cross-Site Scripting (XSS) vulnerability in the HTML export feature of Quill, an open-source rich text editor maintained by Slab. The flaw stems from insufficient data validation when the editor converts user-supplied content into exportable HTML. An attacker can craft malicious input that, once exported and rendered in a browser, executes arbitrary JavaScript in the victim's session context. The issue affects Quill version 2.0.3 and is tracked under CWE-79.
Critical Impact
Successful exploitation enables attackers to execute arbitrary scripts in a victim's browser, leading to session data leakage, UI manipulation, or delivery of secondary payloads through embedded editor content.
Affected Products
- Slab Quill 2.0.3 (Node.js distribution)
- Applications embedding Quill's HTML export functionality
- Downstream web platforms that render Quill-generated HTML without additional sanitization
Discovery Timeline
- 2026-01-13 - CVE-2025-15056 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-15056
Vulnerability Analysis
Quill is a widely deployed WYSIWYG editor used across content management systems, collaboration tools, and web applications. The HTML export feature allows users to convert editor content into raw HTML suitable for storage, transmission, or rendering elsewhere. In version 2.0.3, this export path does not perform adequate validation or encoding of user-supplied content.
An attacker who can insert content into a Quill instance can embed active HTML or script constructs. When the exported HTML is later rendered in a browser context without additional server- or client-side sanitization, the injected script executes. This affects any downstream consumer that trusts Quill output as safe HTML. The vulnerability requires user interaction, since a victim must load or view the exported content for the payload to trigger.
Root Cause
The root cause is missing output encoding and input validation in the HTML export routine (CWE-79). Quill's export path treats certain user-controlled content as trusted markup rather than data. Dangerous constructs, including inline event handlers and script-bearing attributes, are preserved in the exported HTML instead of being neutralized.
Attack Vector
Exploitation occurs over the network and requires user interaction. An attacker with the ability to author or influence Quill editor content, for example through a shared document, comment field, or collaborative workspace, submits a payload containing malicious HTML. When another user triggers the HTML export or views the exported artifact, the browser parses and executes the embedded script. Refer to the Fluid Attacks Security Advisory for a detailed technical description of the exploitation flow.
Detection Methods for CVE-2025-15056
Indicators of Compromise
- Stored Quill documents containing inline event handler attributes such as onerror, onload, or onclick
- Exported HTML artifacts referencing external script sources or javascript: URIs
- Unexpected outbound requests from user browsers immediately after opening exported Quill content
Detection Strategies
- Scan document stores and databases holding Quill content for suspicious HTML patterns, including <script> tags and event handler attributes
- Inspect exported HTML files in content pipelines for active markup that Quill should not emit under normal use
- Enable browser Content Security Policy (CSP) violation reporting to surface script execution attempts originating from exported content
Monitoring Recommendations
- Monitor web application logs for anomalous POST payloads targeting Quill editor endpoints
- Alert on client-side script errors and CSP violations tied to pages rendering user-generated Quill content
- Track version inventory across web applications to identify systems still running Quill 2.0.3
How to Mitigate CVE-2025-15056
Immediate Actions Required
- Inventory all applications embedding Quill and identify instances running version 2.0.3
- Apply server-side HTML sanitization to Quill output before storing or rendering it downstream
- Enforce a strict Content Security Policy that disallows inline scripts and unauthorized script sources
- Review historical Quill content for previously stored malicious payloads
Patch Information
At the time of publication, no fixed version is referenced in the NVD entry for CVE-2025-15056. Monitor the Quill GitHub repository for upstream fixes and release notes. Until a patched release is available, treat Quill HTML export output as untrusted and sanitize it before rendering.
Workarounds
- Post-process exported HTML with a hardened sanitizer such as DOMPurify before rendering in any browser context
- Disable or restrict the HTML export feature for untrusted users where feasible
- Serve rendered Quill content with a restrictive CSP that blocks inline scripts and event handlers
- Isolate rendered user content in a sandboxed iframe with the sandbox attribute to limit script capabilities
# Example Content Security Policy header to reduce XSS impact
Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'none'; frame-ancestors 'none'
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
