SVGO, short for SVG Optimizer, is a Node.js library and command-line application for optimizing SVG files. From version 1.0.0 until versions 2.8.3, 3.3.4, and 4.0.2, the removeScripts plugin, named removeScriptElement in versions 1 through 3, can leave executable content in optimized SVGs because it does not remove namespaced or prefixed script elements such as <svg:script> and, in versions 3 and 4, matches JavaScript URIs case sensitively. Applications that process untrusted SVG input with this plugin enabled and serve the result can allow scripts to execute when another user opens the SVG, exposing local storage or cookies. This issue is fixed in versions 2.8.3, 3.3.4, and 4.0.2.
Affected: npm: svgo
### Summary
SVGO's removeScripts plugin (disabled by default) removes scripts from the SVG, however executable scripts were left intact in some cases. If a consumer relied on this plugin for sanitization and served them to users, these SVGs could open up doors to XSS.
### Details
SVGO has a plugin for removing scripts from an SVG, which removes:
- `<script>` elements - JavaScript URIs (v4 and v3 only) - `on…` event handlers (v4 and v3 only)
While SVGO is not a sanitization library, SVGO continues to maintain the plugin for those already using it for this purpose.
However, there were two problems:
- SVGO did not check namespaced/prefixed `script` elements, for example if one declared an explicit prefix for the SVG namespace ( `<svg:script>`) instead of using the default namespace ( `<script>`), the `<svg:script>` tag would be left intact. - SVGO case sensitively matched JavaScript URIs, but it should've been case-insensitive.
#### Proof of Concept
```js import { optimize } from 'svgo';
/** Presume that this string was obtained in some other way, such as network. */ const original = ` <svg xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg" xmlns:uwu="http://www.w3.org/1999/xlink" viewBox="0 0 100 100" version="1.1"> <a uwu:href="JavaScript:(() => { alert(document.cookie) })();"><text y="30">uwu</text></a> <svg:script> alert(document.cookie); </svg:script> </svg> `;
optimize(original, { plugins: ['removeScripts'] });…
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