CVE-2022-3766 is a Reflected Cross-site Scripting (XSS) vulnerability found in the popular open-source project phpMyFAQ. The security flaw existed in versions prior to 3.1.8, and it allowed attackers to inject malicious scripts into the application, which would then be executed in the context of a user's browser. This issue was present in how user input was handled without proper sanitization.
In this long read, we'll break down how this vulnerability worked, how it could be exploited, and what you can do to keep your systems safe. We'll also see code snippets to understand the mechanics of the bug. All technical explanations are kept simple for broader understanding.
What is Cross-site Scripting (XSS)?
*Cross-site Scripting* (XSS) is a common security bug typically found in web applications. It allows attackers to inject malicious scripts (usually JavaScript) into content that other users will see. This can let attackers steal cookies, hijack sessions, redirect users, or perform other actions as the victim.
DOM-based XSS
CVE-2022-3766 is a *reflected XSS*—where the application immediately responds to a maliciously crafted link, reflecting input back in the page.
Where Was the XSS in phpMyFAQ?
phpMyFAQ is an open-source FAQ system, often used by businesses for self-service support. In versions before 3.1.8, user-supplied input parameters were not always sanitized or escaped before being displayed on the page.
The core of the issue was with parameters received via HTTP GET to some functions (e.g., the action or search functionality). If a user supplied a crafted string, phpMyFAQ would include it in the response HTML—unsanitized—allowing JavaScript execution.
Consider a code snippet *similar* to what was vulnerable (simplified for this post)
// Get parameter from URL
$search = $_GET['search'] ?? '';
// Output user input directly into HTML without sanitation
echo "<input type=\"text\" value=\"$search\">";
If a user opened
https://example.com/index.php?search="><script>alert('XSS')</script>;
The rendered HTML would be
<input type="text" value=""><script>alert('XSS')</script>">
And the JavaScript inside the script tag would run immediately in the victim's browser.
Key Point: The flaw comes from echoing user-data directly into the page—especially into HTML attributes or the DOM—without sanitizing.
`
https://example.com/index.php?search=">alert('Hacked!')
Attacker could do more: Steal cookies, hijack sessions, inject fake forms, or redirect users.
This is called *reflected XSS* because the payload (malicious code) is reflected immediately from the request into the response page.
Here is a sample PoC link (you must have a vulnerable version to try it)
http://your-phpmyfaq-site.tld/index.php?action=search&searchterm=%22%3E%3Cscript%3Ealert('pwned!')%3C/script%3E
Opening that link would pop up an alert box—proof that XSS is possible.
How Was it Fixed?
In the security advisory and the commit correcting the bug, changes were made to ensure that user input is always escaped before being placed into HTML output.
For example, in PHP, htmlspecialchars() is used
echo "<input type=\"text\" value=\"" . htmlspecialchars($search, ENT_QUOTES, 'UTF-8') . "\">";
Now, even with a malicious input, the output will be
<input type="text" value=""><script>alert('XSS')</script>">
So no script gets executed!
References
- GHSA-mh34-hwcp-cpfm Security Advisory — github.com
- NVD — CVE-2022-3766
- Official phpMyFAQ GitHub repository
- What is XSS? OWASP Guide
Final Thoughts
CVE-2022-3766 is another clear example of why web applications must always treat user input as untrusted. Reflected XSS bugs are easy to overlook but can be simple to catch with basic sanitization practices. If you run phpMyFAQ below version 3.1.8, update now!
Timeline
Published on: 10/31/2022 11:15:00 UTC
Last modified on: 11/01/2022 17:41:00 UTC