CVE-2026-27013: Fabric.js SVG Export XSS Vulnerability

CVE-2026-27013 Overview

CVE-2026-27013 is a stored Cross-Site Scripting (XSS) vulnerability in Fabric.js, a popular JavaScript HTML5 canvas library. The vulnerability exists in versions prior to 7.2.0 where the library fails to properly sanitize user-controlled string values when generating SVG output. While the escapeXml() function is applied to text content during SVG export, other user-controlled strings interpolated into SVG attribute markup are not escaped, allowing attackers to inject arbitrary SVG elements including malicious event handlers.

Critical Impact
Attackers can execute arbitrary JavaScript in victim browser sessions through stored XSS when applications accept user-supplied JSON via loadFromJSON() and render the toSVG() output in browser contexts.

Affected Products

Fabric.js versions prior to 7.2.0
Applications using loadFromJSON() with user-supplied data
Systems rendering toSVG() output in browser contexts (SVG previews, exports, email templates, embeds)

Discovery Timeline

2026-02-19 - CVE-2026-27013 published to NVD
2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-27013

Vulnerability Analysis

This vulnerability stems from inconsistent input sanitization in Fabric.js's SVG export functionality. The library correctly applies XML escaping to text content during SVG generation (specifically in src/shapes/Text/TextSVGExportMixin.ts:186), but fails to apply the same protection to other user-controlled string values that are interpolated into SVG attribute markup.

The attack surface is particularly concerning because Fabric.js is commonly used in collaborative design tools, CMS plugins, and web applications that allow users to import and export canvas designs. When an application accepts user-supplied JSON through the loadFromJSON() method and subsequently renders the canvas using toSVG(), the unescaped values can break out of XML attributes and inject arbitrary SVG elements.

This represents a classic stored XSS pattern where the malicious payload is persisted (in the JSON data) and executed when victims view the exported SVG content. The impact includes session hijacking, credential theft, and arbitrary actions performed under the victim's authenticated session.

Root Cause

The root cause is improper input validation (CWE-79) in the SVG export pipeline. While the developers implemented escapeXml() for text content sanitization, they did not apply equivalent protection to all user-controllable string values that flow into SVG attribute contexts. This creates an escape sequence where crafted input can terminate the current attribute context and inject new elements or event handlers directly into the SVG markup.

Attack Vector

The attack requires network access and user interaction to exploit. An attacker crafts malicious JSON containing specially formatted strings designed to break out of SVG attribute contexts. This JSON is loaded into a Fabric.js canvas via loadFromJSON() through various attack surfaces including collaborative sharing features, design import functionality, or CMS plugin interfaces.

When the application subsequently exports the canvas using toSVG() and renders the result in a browser context (such as an SVG preview, downloadable export rendered in-page, email template, or embedded content), the injected SVG elements execute. Malicious event handlers like onload or onclick can trigger arbitrary JavaScript execution in the victim's browser session.

The vulnerability is particularly dangerous in multi-user applications where one user's input is rendered in another user's browser context.

Detection Methods for CVE-2026-27013

Indicators of Compromise

Unusual SVG content containing event handler attributes (onload, onerror, onclick, onmouseover) in Fabric.js exports
JSON payloads with string values containing XML/SVG special characters designed to escape attribute contexts
Unexpected script execution or external resource requests originating from SVG rendering contexts
User-reported suspicious behavior when viewing shared canvas designs or exported SVG files

Detection Strategies

Implement Content Security Policy (CSP) headers to detect and block unauthorized inline script execution
Monitor application logs for unusual patterns in loadFromJSON() calls with suspicious character sequences
Deploy web application firewalls (WAF) with rules to detect SVG injection patterns in JSON payloads
Conduct regular code audits of Fabric.js integration points to identify unsafe data flows

Monitoring Recommendations

Enable browser console monitoring for CSP violation reports indicating XSS attempts
Implement server-side logging of all toSVG() export operations with content inspection
Set up alerting for anomalous patterns in user-generated canvas JSON data
Monitor for reports of unexpected JavaScript behavior in SVG preview or export features

How to Mitigate CVE-2026-27013

Immediate Actions Required

Upgrade Fabric.js to version 7.2.0 or later immediately
Audit all application code paths that use loadFromJSON() with user-supplied data
Review any stored canvas JSON data for potential malicious payloads before processing
Implement additional output encoding for toSVG() results as a defense-in-depth measure

Patch Information

The vulnerability has been addressed in Fabric.js version 7.2.0. The fix ensures that all user-controlled string values interpolated into SVG attribute markup are properly escaped using the escapeXml() function, preventing attribute context escape attacks.

For detailed information about the security fix, refer to the GitHub Security Advisory GHSA-hfvx-25r5-qc3w and the patch commit. The patched version is available at the GitHub Release v7.2.0.

Workarounds

Sanitize all user-supplied JSON data before passing to loadFromJSON() by implementing strict input validation
Apply server-side SVG sanitization to all toSVG() output before rendering in browser contexts
Use DOMPurify or similar libraries to sanitize SVG content before DOM insertion
Implement Content Security Policy headers to mitigate the impact of any successful XSS attempts

bash

# Update Fabric.js to patched version
npm update fabric@7.2.0

# Or install specific patched version
npm install fabric@7.2.0