The /etc/passwd file is used to store unix system users and password information. Attackers can inlude /etc/passwd file in http request to get the unix users and password information, achieving local file inclusion attacks, resulting in unix users and password information leak. This rule requires checking /etc/passwd string in http request to prevent such attacks. This rule supports to defend the A3: Injection of OWASP Top 10 - 2021. Other reference:None