Headline
CVE-2023-22461: Filter Bypass Allows Cross-Site Scripting (XSS)
The sanitize-svg package, a small SVG sanitizer to prevent cross-site scripting attacks, uses a deny-list-pattern to sanitize SVGs to prevent XSS. In doing so, literal <script>-tags and on-event handlers were detected in versions prior to 0.4.0. As a result, downstream software that relies on sanitize-svg and expects resulting SVGs to be safe, may be vulnerable to cross-site scripting. This vulnerability was addressed in v0.4.0. There are no known workarounds
Package
npm sanitize-svg (npm)
Affected versions
<= 0.3.1
Impact
The sanitize-svg package uses a deny-list-pattern to sanitize SVGs to prevent 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
Related news
### 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: ```typescript [...] 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): ```xml <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): ```xml <svg width="500" height="500" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> ...