Phpclanwebsite is prone to a script-injection vulnerability.
An attacker can nest BBCode IMG tags to trigger this issue and execute arbitrary code in a user's browser.
Attacker-supplied HTML and script code would be able to access properties of the site, potentially allowing for theft of cookie-based authentication credentials. Other attacks are also possible.
Reports have not specified which version is vulnerable. The current version (1.23.1) is assumed to be vulnerable; other versions may also be affected.
The following proof of concept is available: