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Security Patrol

IBM i (OS/400, i5/OS)
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Q: I recently received a letter from IBM about some security-related fixes for my AS/400 (see "How Secure Is Your AS/400?" Significa, MC, September 1995). The letter, dated July 21, did not describe the changes. Are you aware of the details? Should I apply the changes?

A: I talked with the IBM security team about the security-related changes. IBM recognizes that, with the increased interconnection of AS/400s (including the Internet), there is an increased risk from outside hackers. These PTFs help reduce the security exposures, and you should apply them to your system. I'll explain the details of the changes made when you apply the PTFs, but first let me recommend that all AS/400 installations take the following steps immediately to reduce security exposures:

1. Order the security PTF associated with the different OS/400 releases listed in 1 and you automatically receive any corequisite PTFs. Apply all the PTFs that you receive.

1. Order the security PTF associated with the different OS/400 releases listed in Figure 1 and you automatically receive any corequisite PTFs. Apply all the PTFs that you receive.

2. Change all default passwords.

3. Install an exit program to prevent use of the Submit Remote Command (SBMRMTCMD) command. If preventing remote commands is not possible, use the exit program to record the remote commands and review the commands.

4. Increase system security level to 40.

The following details and background information explain why the changes should be made.

Change Default Passwords

The PTF cover letter recommends that you change the password of all IBM profiles. This is very important, as illustrated by the following actual experience.

When I do a security review on clients' AS/400s, I sometimes try to guess the password of some of the IBM-provided user profiles. I often find the password of the QSRV user profile is left unchanged or is some trivial value such as IBM or SERVICE.

The default passwords for all IBM profiles and any vendor software should be changed or set to *NONE. It is critical that you change the password for the following IBM system-supplied profiles: QSECOFR, QSRV, QSRVBAS, QPGMR, QUSER, and QSYSOPR. The user profile QSRV is a large exposure because installations fail to change the password, and the QSRV profile can use service tools to view and modify any object on the system. Eliminating trivial and default passwords is essential to protecting your AS/400.

Prevent Remote Commands

A method to gain access to a remote AS/400 is to create a DDM file. The DDM file can be used on SBMRMTCMD to issue commands on the remote system. If the remote system does not include an exit program to prevent remote commands, the commands are run as the default user (usually the QUSER user profile). SBMRMTCMD can also be used to send commands to the remote system. These commands could display information about communication connections. Then the print files could be sent back to the local AS/400.

I recommend creating an exit program to prevent the use of remote commands on your AS/400 (see 2 for a sample exit program). The exit program is specified on the DDM request access (DDMACC) parameter of the Change Network Attributes (CHGNETA) command. For more information on restricting DDM users' access to your system through exit programs, see the Distributed Data Management manual.

I recommend creating an exit program to prevent the use of remote commands on your AS/400 (see Figure 2 for a sample exit program). The exit program is specified on the DDM request access (DDMACC) parameter of the Change Network Attributes (CHGNETA) command. For more information on restricting DDM users' access to your system through exit programs, see the Distributed Data Management manual.

Limit Configuration Commands

One of the changes made by the IBM PTF limits access to the commands that can be used to configure APPC communications. The *PUBLIC access to these commands is revoked, preventing the QUSER user profile from being able to create or change APPC configuration objects on a target system. After the PTF is applied, the user must have authority to the commands and object management (*OBJMGT) authority to change any existing APPC configuration object. When you apply the PTF for a V3R1 system, the commands required to configure APPC communications will require the special authority *IOSYSCFG in addition to *OBJMGT authority.

Limit Access to QCPFMSG

The PTF changes the *PUBLIC access to the message file QCPFMSG to *USE. Some OS/400 components retrieve messages from QCPFMSG which represent the commands issued when a user selects an option from an IBM menu. With *CHANGE access, a hacker could possibly change the message file to cause a different command to be issued.

Change to Security Level 40

Most AS/400 installations use security level 30. However, security level 40 provides some important protections. (Moving to level 40 is described in "A Guide to Changing QSECURITY," MC, March 1994.) For instance, with level 40, jobs submitted with a JOBD (job description) that names a user profile require that the user have access to both the JOBD and the user profile. If you are not running level 40 security, a hacker can find a JOBD that names a user profile and use that JOBD to run jobs as another user. For example, the user profile for the QBATCH JOBD in library QGPL is QPGMR, and QPGMR usually has a significant degree of authority.

References

Client Access/400 for DOS and OS/2 Technical Reference (SC41-3563, CD-ROM QBKAKV01).

Distributed Data Management (SC41-3307, CD-ROM QBKALH00).

Security Reference (SC41-3302, CD-ROM QBKALC00).

Security Patrol

Figure 1: Security PTFs

 OS/400 PTF Number Release V3R1 SF23871 V3R0M5 SF23873 V2R3 SF23874 V2R2 SF24390 
 
Security Patrol 
 
Figure 2: Exit Program RMT001CL
 
 /**************************************************************************/ /* Installation instructions */ /* 1. Compile program */ /* CRTCLPGM PGM(XXX/RMT001CL) SRCFILE(QCLSRC) */ /* 2 Change network attributes to specify exit program */ /* CHGNETA DDMACC(XXX/RMT001CL) PCSACC(XXX/RMT001CL) */ /* */ /* The program will write entries in the audit journal QAUDJRN. */ /* 'X1' = Requests that are allowed (*LMSRV not logged) */ /* 'X0' = Requests that are rejected */ /**************************************************************************/ PGM PARM(&RC &STRUC) DCL VAR(&RC) TYPE(*CHAR) LEN(1) /*Return code + 1=allow, 0=prevent */ DCL VAR(&STRUC) TYPE(*CHAR) LEN(174) /*Request + description */ DCL VAR(&USER) TYPE(*CHAR) LEN(10) DCL VAR(&APP1) TYPE(*CHAR) LEN(10) DCL VAR(&APP2) TYPE(*CHAR) LEN(10) DCL VAR(&ENTTYP) TYPE(*CHAR) LEN(2) MONMSG MSGID(CPF0000) EXEC(GOTO CMDLBL(EXIT)) CHGVAR VAR(&RC) VALUE('1') /* Allow request */ CHGVAR VAR(&USER) VALUE(%SST(&STRUC 1 10)) CHGVAR VAR(&APP1) VALUE(%SST(&STRUC 11 10)) CHGVAR VAR(&APP2) VALUE(%SST(&STRUC 21 10)) /************************************************/ /* Do not log IBM request to check license */ /************************************************/ IF COND(&APP1 = '*LMSRV') THEN(GOTO CMDLBL(EXIT)) /************************************************/ /* Allow requests for selected users */ /************************************************/ IF COND(&USER = 'XXXXXXXXX') THEN(GOTO + CMDLBL(LOG)) /***********************************************/ /* Prevent use of remote commands */ /***********************************************/ IF COND(&APP1 = '*DDM' *AND &APP2 = 'COMMAND') + THEN(DO) CHGVAR VAR(&RC) VALUE('0') GOTO CMDLBL(LOG) ENDDO /************************************************/ /* Prevent file down upload from PC users */ /************************************************/ IF COND(&APP1 = '*TFRCTL' *AND &APP2 = + 'REPLACE') THEN(DO) CHGVAR VAR(&RC) VALUE('0') GOTO CMDLBL(LOG) ENDDO /******************************************************/ /* Log request X1=allow request X0=prevent request */ /******************************************************/ LOG: CHGVAR VAR(&ENTTYP) VALUE('X' *CAT &RC) SNDJRNE JRN(QAUDJRN) TYPE(&ENTTYP) ENTDTA(&STRUC) EXIT: ENDPGM
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