Affected versions
Symfony UX Icons versions >=2.17.0<2.36.1, >=3.0.0<3.2.0 are affected by this security issue.
The issue has been fixed in Symfony UX Icons 2.36.1, 3.2.0.
Description
The ux_icon() Twig function is marked is_safe=['html'], so Twig
never escapes its output. Icon::toHtml() inlines the SVG source verbatim
into the page. Browsers execute <script> elements and on*
event-handler attributes found inside inline SVG, making any unsanitized
icon a vector for cross-site scripting.
Two code paths were affected. In the local file path, Icon::fromFile()
only stripped <script> elements that were direct children of <svg>,
leaving nested scripts and all on* attributes untouched despite a code
comment claiming broader protection. In the Iconify on-demand path (enabled
by default), the remote JSON body field was wrapped into an Icon
object with no sanitization at all. Concrete attack vectors include a
malicious SVG icon pack from a third-party theme or downloaded icon set, or
a controlled Iconify endpoint configured via iconify.endpoint (including
a poisoned cache).
Resolution
Introducing an IconFactory that centralizes sanitization across every
icon source before an Icon object is created. The sanitizer removes
script-capable elements (script, foreignObject, iframe,
object, embed), SMIL animations targeting on*, href, or
xlink:href attributes, CDATA sections, processing instructions, all
on* attributes, and javascript:, vbscript:, and
data:text/html URL schemes.
<style> elements are kept for theming but have any handlers stripped.
Icons that contain none of these constructs are byte-for-byte identical
after sanitization.
Credits
We would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.