OCO-Server is a self-hosted endpoint management application for computer inventory, software deployment, and mobile device management. Prior to 1.2.1, Html::commandButton() in lib/Html.class.php embeds an action URL containing a stored computer hostname into a JavaScript string in an inline onclick handler, using htmlspecialchars(ENT_QUOTES) only for HTML escaping. Browsers decode the HTML entities before interpreting the handler as JavaScript, allowing a crafted hostname to escape the string and execute script in an administrator's authenticated session when an affected command button is activated. frontend/views/computer-details.php passes $computer->hostname to this helper using Computer::DEFAULT_COMPUTER_COMMANDS in lib/Models/Computer.class.php, whose VNC, RDP, SSH, and Ping entries use new_tab=false and the vulnerable window.location branch. A remote attacker who possesses the shared agent-registration-key can use the oco.agent.hello handler in frontend/api-agent.php to store an unchecked hostname when agent-self-registration-enabled is enabled; self-registration is disabled by default. The vulnerable default command buttons require no custom command configuration. The injected script can abuse the administrator's privileges, including permission to deploy software jobs to managed computers. This issue is fixed in version 1.2.1.