Yonyou U8 CRM contains an unauthenticated SQL injection vulnerability in the fillbacksettingedit.php configuration endpoint where the DontCheckLogin=1 parameter bypasses authentication and the id parameter is incorporated into SQL queries without sanitization. Attackers can exploit this flaw to execute arbitrary SQL commands and, on Microsoft SQL Server deployments with xp_cmdshell enabled, write backdoor files and execute arbitrary operating system commands. Exploitation evidence was first observed by the Shadowserver Foundation on 2025-02-13.