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Security Patrol

IBM i (OS/400, i5/OS)
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Q: We recently implemented Advanced Peer-to-Peer Net-working (APPN) connectivity between a network of about 40 AS/400s. In the process of experimenting with the Submit Remote Command (SBMRMTCMD) command, I found that I was able to submit commands on a remote system without even having a password.

Both systems are running at security level 30. On the remote system, we use a default user profile that has PASSWORD(*NONE), yet we were able to submit commands.

I have discovered that I can block this by changing the DDM request access (DDMACC) network attribute on the target system to *REJECT. However, this also blocks a function we need. Is there a way to limit the use of SBMRMTCMD?

A: There is a way to prevent the use of the SBMRMTCMD command and the Client Access/400 Remote Command (RMTCMD) program other than setting the DDMACC network attribute to *REJECT. You can specify the name of a user exit program in the DDMACC network attribute of the target system. The program will supplement AS/400 object level security and determine whether to allow a request from a remote system. The user exit program is passed a structure (shown in 1) that describes the type of request. There are additional fields in the structure, but the first 30 bytes are all that is needed to determine if the request is a remote command.

A: There is a way to prevent the use of the SBMRMTCMD command and the Client Access/400 Remote Command (RMTCMD) program other than setting the DDMACC network attribute to *REJECT. You can specify the name of a user exit program in the DDMACC network attribute of the target system. The program will supplement AS/400 object level security and determine whether to allow a request from a remote system. The user exit program is passed a structure (shown in Figure 1) that describes the type of request. There are additional fields in the structure, but the first 30 bytes are all that is needed to determine if the request is a remote command.

The exit program STOPCMDS (shown in 2) looks at the structure to determine if the request is a command (sent by SBMRMTCMD or RMTCMD) and, if so, prevents the request by setting the return code. The subapplication function of 'COMMAND' indicates that a command string is submitted by SBMRMTCMD from another AS/400 or RMTCMD from Client Access. After you have created the program in 2, assign it to the DDMACC network attribute with the following command:

The exit program STOPCMDS (shown in Figure 2) looks at the structure to determine if the request is a command (sent by SBMRMTCMD or RMTCMD) and, if so, prevents the request by setting the return code. The subapplication function of 'COMMAND' indicates that a command string is submitted by SBMRMTCMD from another AS/400 or RMTCMD from Client Access. After you have created the program in Figure 2, assign it to the DDMACC network attribute with the following command:

CHGNETA DDMACC(XXX/STOPCMDS)

If you want to read more, the details of the exit program are in the V3R1 Distributed Data Management guide (SC41-3307, CD-ROM QBKAHL00).

Q: I have certain users who need *SPLCTL special authority on the AS/400 to allow them to start or vary on printers. The problem is, if they are given this authority, they have the ability to view all spool files, which can give them access to some sensitive information. Is there a way to give a user the authority to start and vary on printers without giving them the ability to view spool files?

A: One of the most common security problems that I see on systems is too many users with *SPLCTL authority. You do not need to give users *SPLCTL authority to allow them to start print writers. There are two alternatives that can be employed.

The first alternative is to give users special authority of *JOBCTL rather than *SPLCTL.

The attributes of an output queue are important when securing spooled files (see Security Patrol, MC, March 1995 for a full description of how the output queue attributes interact with printing functions). The default attributes for creating an output queue are DSPDTA(*NO) OPRCTL(*YES) AUTCHK(*OWNER). A user who has *JOBCTL special authority can start and stop the print writers associated with output queues created with these attributes; *SPLCTL authority is not required.

Sensitive output that you do not want users with *JOBCTL authority to display should be sent on an output queue with increased security. The attributes of a secure output queue should be DSPDTA(*NO or *OWNER) OPRCTL(*NO) and AUTCHK(*OWNER).

Only the owner of the output queue and users with *SPLCTL authority can view spool files that reside in secured (as described above) output queues. If the output queue is owned by a group profile that has *USE access to the printer device description, then all members of the group can start a print writer and display the spool files on this output queue.

The second option does not give users *JOBCTL special authority. Instead it adopts authority when starting print writers.

If you are reluctant to give users *JOBCTL authority because the user can access other users' jobs, then you can create two CL programs (as shown in 3 and 4) that adopt the authority of a user who has *JOBCTL. The function of these two CL programs (STRWTR1 and ENDWTR1) is to allow the user to start or stop print writers.

If you are reluctant to give users *JOBCTL authority because the user can access other users' jobs, then you can create two CL programs (as shown in Figure 3 and Figure 4) that adopt the authority of a user who has *JOBCTL. The function of these two CL programs (STRWTR1 and ENDWTR1) is to allow the user to start or stop print writers.

The Work with Writers (WRKWTR) command has options to start and stop a print writer, but it also has a command line. You should not allow the user access to a command line while adopting authority, and that is why two programs are required.


Security Patrol

Figure 1: Parameter List for User Exit Program

 Field Type Len Description User Char 10 User profile name of target DDM job. Application Char 10 Application name: '*DDM ' for Distributed Data Management Subapplication Char 10 Requested function: 'ADDMBR ' 'DELETE ' 'RENAME ' 'CHANGE ' 'EXTRACT ' 'RGZMBR ' 'CHGMBR ' 'INITIALIZE' 'RMVMBR ' 'CLEAR ' 'LOAD ' 'RNMMBR ' 'COMMAND ' 'LOCK ' 'UNLOAD ' 'COPY ' 'MOVE ' 'CREATE ' 'OPEN 
Security Patrol

Figure 2: CL Program STOPCMDS

 /*===============================================================*/ /* To compile: */ /* */ /* CRTCLPGM PGM(XXX/STOPCMDS) SRCFILE(XXX/QCLSRC) */ /* */ /*===============================================================*/ PGM PARM(&RTNCODE &DATA) DCL VAR(&RTNCODE) TYPE(*CHAR) LEN(1) DCL VAR(&DATA) TYPE(*CHAR) LEN(30) DCL VAR(&APPL) TYPE(*CHAR) LEN(10) CHGVAR VAR(&APPL) VALUE(%SST(&DATA 21 10)) IF COND(&APPL = COMMAND) THEN(CHGVAR + VAR(&RTNCODE) VALUE(0)) ELSE CMD(CHGVAR VAR(&RTNCODE) VALUE(1)) ENDPGM 
Security Patrol

Figure 3: CL Program STRWTR1

 /*===============================================================*/ /* To compile: */ /* */ /* CRTCLPGM PGM(XXX/STRWTR1) SRCFILE(XXX/QCLSRC) + */ /* USRPRF(*OWNER) */ /* */ /*===============================================================*/ PGM ?STRPRTWTR ENDPGM 
Security Patrol

Figure 4: CL Program ENDWTR1

 /*===============================================================*/ /* To compile: */ /* */ /* CRTCLPGM PGM(XXX/ENDWTR1) SRCFILE(XXX/QCLSRC) + */ /* USRPRF(*OWNER) */ /* */ /*===============================================================*/ PGM ?ENDWTR ENDPGM 
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