auth_password(Authctxt *authctxt, const char *password)
{
	struct passwd * pw = authctxt->pw;
	int result, ok = authctxt->valid;
#if defined(USE_SHADOW) && defined(HAS_SHADOW_EXPIRE)
 	static int expire_checked = 0;
 #endif
 
	if (strlen(password) > MAX_PASSWORD_LEN)
		return 0;

 #ifndef HAVE_CYGWIN
 	if (pw->pw_uid == 0 && options.permit_root_login != PERMIT_YES)
 		ok = 0;
#endif
	if (*password == '\0' && options.permit_empty_passwd == 0)
		return 0;

#ifdef KRB5
	if (options.kerberos_authentication == 1) {
		int ret = auth_krb5_password(authctxt, password);
		if (ret == 1 || ret == 0)
			return ret && ok;
		/* Fall back to ordinary passwd authentication. */
	}
#endif
#ifdef HAVE_CYGWIN
	{
		HANDLE hToken = cygwin_logon_user(pw, password);

		if (hToken == INVALID_HANDLE_VALUE)
			return 0;
		cygwin_set_impersonation_token(hToken);
		return ok;
	}
#endif
#ifdef USE_PAM
	if (options.use_pam)
		return (sshpam_auth_passwd(authctxt, password) && ok);
#endif
#if defined(USE_SHADOW) && defined(HAS_SHADOW_EXPIRE)
	if (!expire_checked) {
		expire_checked = 1;
		if (auth_shadow_pwexpired(authctxt))
			authctxt->force_pwchange = 1;
	}
#endif
	result = sys_auth_passwd(authctxt, password);
	if (authctxt->force_pwchange)
		disable_forwarding();
	return (result && ok);
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.