Language: PHP
Label: safe
CWE: CWE-79 \u2014 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Code:
    public function validate($string, $config, $context)
    {
        if ($this->valid_values === false) {
            $this->valid_values = $config->get('Attr.AllowedFrameTargets');
        }
        return parent::validate($string, $config, $context);
    }