Are you seeing this appearing in your own website's or logs , or were you trying to test a specific platform's security? PHP md5() function - Scaler Topics
If the string f91289c99fe56ec5f183dfefe39ecda8 appears on the page after posting, it proves the site is insecure and could be fully compromised by an attacker. ${@var_dump(md5(120902694))};
Specifically, the command var_dump(md5(120902694)) tells the server to calculate a unique fingerprint (an MD5 hash ) for that number and display the result along with its data type. Are you seeing this appearing in your own