Cross-Site Scripting in Fabric.js SVG Serialization

Detection Guidance

This vulnerability involves improper escaping of user-controlled input in the color field of the colorStops array within fabric.Gradient objects when serialized to SVG via the toSVG() method. Detection involves identifying if your system uses a vulnerable version of Fabric.js (prior to 7.4.0) and if it processes or renders SVG strings generated by fabric.Gradient objects.

To detect potential exploitation attempts or presence of the vulnerability, you can search for SVG strings containing suspicious or malformed color attributes that include injected HTML or JavaScript payloads.

Suggested commands include:

• On systems storing or logging SVG content, use grep or similar tools to find suspicious patterns, for example: grep -rE 'colorStops.*".*\"><img|onerror' /path/to/logs_or_files
• In web application codebases, check the Fabric.js version by inspecting package.json or equivalent: grep 'fabric' package.json
• Use browser developer tools to inspect SVG elements generated by Fabric.js and look for unescaped attributes in <stop> elements within gradients.

Ultimately, upgrading Fabric.js to version 7.4.0 or later is the recommended mitigation.

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Compliance Impact

The vulnerability in Fabric.js allows for Cross-Site Scripting (XSS) attacks due to improper escaping of user input during SVG serialization. Such XSS vulnerabilities can lead to unauthorized execution of JavaScript in users' browsers, potentially exposing sensitive data or enabling further attacks.

While the CVE description does not explicitly mention compliance with standards like GDPR or HIPAA, XSS vulnerabilities can impact compliance by risking the confidentiality and integrity of personal or sensitive data handled by affected applications.

Organizations using vulnerable versions of Fabric.js may face challenges in meeting security requirements mandated by these regulations, as they require protection against unauthorized data access and ensuring secure handling of user data.

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Executive Summary

This vulnerability exists in Fabric.js, a Javascript HTML5 canvas library, prior to version 7.4.0. It is a Cross-Site Scripting (XSS) issue caused by improper escaping of user-controlled input during SVG serialization via the toSVG() method. Specifically, the color field within the colorStops array of a fabric.Gradient object is not properly escaped when converted into SVG <stop> elements. This flaw allows an attacker to inject arbitrary HTML or SVG code, which can then execute JavaScript in the victim's browser if the generated SVG string is rendered into the DOM.

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Impact Analysis

This vulnerability can allow an attacker to execute arbitrary JavaScript code in the context of the victim's browser. This can lead to various malicious actions such as stealing sensitive information, hijacking user sessions, performing actions on behalf of the user, or delivering further malware. The impact is limited to confidentiality and integrity as indicated by the CVSS score, with no direct impact on availability.

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Mitigation Strategies

To mitigate this vulnerability, update Fabric.js to version 7.4.0 or later, where the issue with improper escaping in the toSVG() method has been fixed.

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