string grantAccess = @"runas /savecred /user:domainuser1 ""icacls \ext.kfgdfsGroupFTPData_Exchange" + login + @" /grant: GFKD-RE-AP-RT-GIM-USER:(OI)(CI)(RC,RD,WD,AD,REA,WEA,X,DC,RA,WA)""";

Process.Start("cmd.exe", grantAccess);

string grantAccess = @"/savecred ""icacls \ext.gfkdfsGroupFTPData_Exchange" + login + @" /grant: GFKD-RE-AP-RT-GIM-USER:(OI)(CI)(RC,RD,WD,AD,REA,WEA,X,DC,RA,WA)""";

Process processGrant = new Process();
ProcessStartInfo startInfoGrant = new ProcessStartInfo();
startInfoGrant.Domain = "domain";
startInfoGrant.UserName = "user1";
startInfoGrant.Password = userPassword; // this is a SecureString
startInfoGrant.FileName = "cmd.exe";
startInfoGrant.Verb = "runas";          // I've tried it with or without this line
startInfoGrant.Arguments = grantAccess;
startInfoGrant.CreateNoWindow = true;
startInfoGrant.UseShellExecute = false;
processGrant.StartInfo = startInfoGrant;
processGrant.Start();
processGrant.WaitForExit();