To setup the problem, edit /etc/nsswith.conf and add 'db' first, for example
-passwd files sss
+passwd db files sss

  Then, this example program will crash if setpwent is not called:

"""
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>

void main()
{
    int usercnt;
    int grpcnt;
    struct passwd *p;

    // setpwent();  not absolutely required but good practice
    p = getpwent();
    for(usercnt = 0; p; p = getpwent(), usercnt++);
    endpwent();

//    setpwent(); if uncomment it the code does not segfault
    p = getpwent();
    for(usercnt = 0; p; p = getpwent(), usercnt++) {
        printf("%s (%d)\tHOME %s\tSHELL %s\n", p->pw_name, p->pw_uid, p->pw_dir, p->pw_shell);
    }
    setpwent();
}
"""

  If not using passwd.db apparently the default behaviour is to have
endpwent to implicitly rewind, so, setpwent is somewhat useless other
than when using a database.

  Is the crash (due to reading past the end of the stream) expected?