#41 Incorrect password during login makes twice login attempts

[Ramkumar]

Hi,
We are using netconf 3PP to establish our communcation to the node and exchanges netconf messages. Netconf internally uses JSch to establish SSH connection.

It is found that it uses UserAuthKeyboardInteractive method and in this method, when the password provided is incorrect, the login is attempted again i.e for two times, then only the controlled is moved out and incorrect login error is displayed.

So, for a single incorrect login attempt, the code tries two login attempt before displaying the error. Since we are using pam_tally2 to monitor the login attempts and have some password lockout configurations policies, the count is incremented twice for single attempt and user lockout is reached quickly.

Could you please let us know is there a way to correct it.?

Below is the problematic code "UserAuthKeyboardInteractive.java".
The code resets the password it is trying after the first attempt, but the attempt is made for the second time, since the pam_tally2 counts only the login attempts made to the node, the failure count is incremented twice.

package com.jcraft.jsch;

class UserAuthKeyboardInteractive extends UserAuth{
public boolean start(Session session) throws Exception{
super.start(session);

if(userinfo!=null && !(userinfo instanceof UIKeyboardInteractive)){
  return false;
}

String dest=username+"@"+session.host;
if(session.port!=22){
  dest+=(":"+session.port);
}
byte[] password=session.password;

boolean cancel=false;

byte[] _username=null;
_username=Util.str2byte(username);

while(true){

  if(session.auth_failures >= session.max_auth_tries){
return false;
  }

  // send
  // byte      SSH_MSG_USERAUTH_REQUEST(50)
  // string    user name (ISO-10646 UTF-8, as defined in [RFC-2279])
  // string    service name (US-ASCII) "ssh-userauth" ? "ssh-connection"
  // string    "keyboard-interactive" (US-ASCII)
  // string    language tag (as defined in [RFC-3066])
  // string    submethods (ISO-10646 UTF-8)
  packet.reset();
  buf.putByte((byte)SSH_MSG_USERAUTH_REQUEST);
  buf.putString(_username);
  buf.putString(Util.str2byte("ssh-connection"));
  //buf.putString("ssh-userauth".getBytes());
  buf.putString(Util.str2byte("keyboard-interactive"));
  buf.putString(Util.empty);
  buf.putString(Util.empty);
  session.write(packet);

  boolean firsttime=true;
  loop:
  while(true){
    buf=session.read(buf);
    int command=buf.getCommand()&0xff;

if(command==SSH_MSG_USERAUTH_SUCCESS){
  return true;
}
if(command==SSH_MSG_USERAUTH_BANNER){
  buf.getInt(); buf.getByte(); buf.getByte();
  byte[] _message=buf.getString();
  byte[] lang=buf.getString();
  String message=Util.byte2str(_message);
  if(userinfo!=null){
    userinfo.showMessage(message);
  }
  continue loop;
}
if(command==SSH_MSG_USERAUTH_FAILURE){
  buf.getInt(); buf.getByte(); buf.getByte();
  byte[] foo=buf.getString();
  int partial_success=buf.getByte();

// System.err.println(new String(foo)+
// " partial_success:"+(partial_success!=0));

  if(partial_success!=0){
    throw new JSchPartialAuthException(Util.byte2str(foo));
  }

  if(firsttime){
    return false;
    //throw new JSchException("USERAUTH KI is not supported");
    //cancel=true;  // ??
  }
      session.auth_failures++;
  break;
}
if(command==SSH_MSG_USERAUTH_INFO_REQUEST){
  firsttime=false;
  buf.getInt(); buf.getByte(); buf.getByte();
  String name=Util.byte2str(buf.getString());
  String instruction=Util.byte2str(buf.getString());
  String languate_tag=Util.byte2str(buf.getString());
  int num=buf.getInt();
  String[] prompt=new String[num];
  boolean[] echo=new boolean[num];
  for(int i=0; i<num; i++){
    prompt[i]=Util.byte2str(buf.getString());
    echo[i]=(buf.getByte()!=0);
  }

  byte[][] response=null;

      if(password!=null &&
         prompt.length==1 &&
         !echo[0] &&
         prompt[0].toLowerCase().indexOf("password:") >= 0){
        response=new byte[1][];
        response[0]=password;
        password=null;
      }
      else if(num>0
     ||(name.length()>0 || instruction.length()>0)
     ){
    if(userinfo!=null){
          UIKeyboardInteractive kbi=(UIKeyboardInteractive)userinfo;
          String[] _response=kbi.promptKeyboardInteractive(dest,
                                                           name,
                                                           instruction,
                                                           prompt,
                                                           echo);
          if(_response!=null){
            response=new byte[_response.length][];
            for(int i=0; i<_response.length; i++){
              response[i]=Util.str2byte(_response[i]);
            }
          }
    }
  }

  // byte      SSH_MSG_USERAUTH_INFO_RESPONSE(61)
  // int       num-responses
  // string    response[1] (ISO-10646 UTF-8)
  // ...
  // string    response[num-responses] (ISO-10646 UTF-8)
  packet.reset();
  buf.putByte((byte)SSH_MSG_USERAUTH_INFO_RESPONSE);
  if(num>0 &&
     (response==null ||  // cancel
      num!=response.length)){

        if(response==null){
          // working around the bug in OpenSSH ;-<
          buf.putInt(num);
          for(int i=0; i<num; i++){
            buf.putString(Util.empty);
          }
        }
        else{
          buf.putInt(0);
        }

    if(response==null)
      cancel=true;
  }
  else{
    buf.putInt(num);
    for(int i=0; i<num; i++){
      buf.putString(response[i]);
    }
  }
  session.write(packet);
      /*
  if(cancel)
    break;
      */
  continue loop;
}
//throw new JSchException("USERAUTH fail ("+command+")");
return false;
  }
  if(cancel){
throw new JSchAuthCancelException("keyboard-interactive");
//break;
  }
}
//return false;

}
}