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Harden dashboard welcome message against XSS #106

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Harden dashboard welcome message against XSS #106

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66 changes: 65 additions & 1 deletion src/Http/Controllers/DashboardAdminController.php
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

namespace TypiCMS\Modules\Core\Http\Controllers;

use DOMDocument;
use Illuminate\Http\RedirectResponse;
use Illuminate\Support\Facades\Http;
use Illuminate\View\View;
Expand Down Expand Up @@ -34,12 +35,75 @@ private function fetchWelcomeMessage(): string
$body = rescue(fn () => Http::timeout(2)->get($url)->body());

if ($body !== null) {
return strip_tags($body, '<a><strong><em><br><p><ul><ol><li>');
return $this->sanitizeHtml($body);
}

return $fallback;
}

/**
* Sanitize remotely fetched HTML before it is rendered unescaped in the
* dashboard. Beyond limiting the allowed tags, every attribute is removed
* so that event handlers (onclick, onerror, …) and javascript: URIs cannot
* be smuggled in through a compromised or man-in-the-middled upstream. Only
* a safe href is restored on links.
*/
private function sanitizeHtml(string $html): string
{
$html = strip_tags($html, '<a><strong><em><br><p><ul><ol><li>');

if (mb_trim($html) === '') {
return '';
}

$dom = new DOMDocument;
libxml_use_internal_errors(true);
$dom->loadHTML(
'<?xml encoding="UTF-8" ?><body>'.$html.'</body>',
LIBXML_NOERROR | LIBXML_NOWARNING,
);
libxml_clear_errors();

foreach (iterator_to_array($dom->getElementsByTagName('*')) as $element) {
$href = mb_strtolower($element->tagName) === 'a' ? $element->getAttribute('href') : null;

while ($element->attributes->length > 0) {
$element->removeAttribute($element->attributes->item(0)->nodeName);
}

if ($href !== null && $this->isSafeHref($href)) {
$element->setAttribute('href', $href);
}
}

$body = $dom->getElementsByTagName('body')->item(0);
$output = '';
if ($body) {
foreach ($body->childNodes as $child) {
$output .= (string) $dom->saveHTML($child);
}
}

return mb_trim($output);
}

private function isSafeHref(string $href): bool
{
$href = mb_trim($href);

if ($href === '') {
return false;
}

if (str_starts_with($href, '/') || str_starts_with($href, '#')) {
return true;
}

$scheme = mb_strtolower((string) parse_url($href, PHP_URL_SCHEME));

return in_array($scheme, ['http', 'https', 'mailto'], true);
}

private function isAllowedUrl(string $url): bool
{
$parsed = parse_url($url);
Expand Down