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Tuesday, August 14, 2007

SAP R/3 System Parameters Review

This overview describes how security and controls can be implemented through system parameters. System parameters are used to maintain configuration over the operation of the SAP system. System parameters may define key settings for the whole system on which SAP runs, individual hosts systems (e.g. configuration for only one of many application servers)

or the instances that are running on these servers. The majority of system parameters ensure that SAP operates effectively on the customer’s preferred hardware, operating system and database platforms. System parameters also control how SAP operates and provides system wide control over some aspects of Security. System parameters are set using transaction RZ10. To make the parameters globally effective set them in the default profile, DEFAULT.PFL. To make them instance-specific, you must set them in the profiles of each application server in your R/3 System. System parameters can be reviewed with transaction TU02 or from the standard SAP report RSPARAM using transaction SA38.

Incorrect Logon, Default Clients and Default Start Menus

• Login/fails_to_session_end (default value - 3) defines the number of times a user can enter an incorrect password before the system terminates the logon attempt.

• Login/fails_to_user_lock (default value - 12) the number of times a user can enter an incorrect password before the system locks the user. If the system locks, an
entry is written to the system log, and the lock is released at midnight.

• Login/failed_user_auto_unlock (default value - 1) unlocks users who are locked by logging on incorrectly. The locks remain if the parameter value is 0.

• Login/system_client This parameter specifies the default client. This client is automatically filled in on the system logon screen. Users can enter a different client.

Login/ext_security Since release 3.0E, external security tools such as Kerberos or Secude have managed R/3 System access. If this parameter is set, an additional identification can be specified for each user (in user maintenance) where users log on
to their security system. To activate, set the value to X.

• rdisp/gui_auto_logout (default value - 0) Maximum time allowed between input from the GUI before the frontend is automatically logged out. The value is set in seconds and the value of zero is used when this facility is not active.

• Start_menu This parameter specifies the default start menu for all users and can be overwritten with the user-specific start menu (transaction SU50). The default is S000, and this value can be set to any other area menu code.

Password Security
System profile parameters define the minimum length of a password and the frequency with which users must change passwords.

Login/min_password_lng minimum password length. The minimum is three characters and the maximum eight characters.

Login/password_expiration_time number of days after which a password must be changed. The parameter allows users to keep their passwords without time limit and leaves the value set to the default, 0.

• To prevent use of a certain password, enter it in table USR40. Maintain this table with transaction SM30. In USR40, you may also generically specify prohibited passwords.

There are two wild-card characters:
– ? means a single character
– * means a sequence of any combination characters of any length

Examples:
– 123* in table USR40 prohibits any password that begins with the sequence 123.
– *123* prohibits any password that contains the sequence 123.
– AB? prohibits passwords that begin with AB and have an additional character, such as ABA, ABB, and
ABC.

Securing SAP* user master record

• login/no_automatic_user_sapstar By default SAP is installed with a user master record SAP*. This user has the profile SAP_ALL with access to all transactions and programs in SAP. By default if this user master record is deleted then SAP allows logon using SAP* and a password of ‘PASS’. Although the user master record does not exist, SAP grants unrestricted system access privileges to SAP*. By setting this parameter value to ‘1’ this ‘backdoor’ access is blocked in the event the SAP* user master record is deleted. Prior to version 4.0 this parameter was login/no_automatic_user_sap*.

Tracing Authorisations

• Auth/check_value_write_on (default value - 0) Authorization failures can be evaluated immediately they occur by running transaction SU53. This functionality is only active if the parameter is set to a value greater than zero in the system profile parameter.

• Auth/authorization_trace (version 4.0B onwards - default value - ‘N’) When the parameter is set, any authorization checks performed are validated against existing entries in table USOBX. If the table does not contain the transaction/authorization object combination, then a new entry is added to the SAP reference table (i.e. USOBT not USOBT_C). Due to significant performance issues, SAP does not recommend this parameter being set in customer systems.

• Auth/test_mode (version 4.0B onwards - default value ‘N’)
When activated every authority check starts report RSUSR400. However SAP recommends not activating this parameter as the system is paralyzed if syntax errors occur in running the report and it has a significant performance impact .

Authority Check De-activation
• Auth/no_check_on_sucode (version 3.0E to version 3.1H - default value ‘N’), Auth/no_check_on_tcode (version 4.0 onwards - default value - ‘N’) From release 3.0E, the system checks on object S_TCODE. In upgrades from versions prior to 3.0E to set this flag
to ‘Y’ to ensure that old profiles operate in the new system. By default, the function is inactive.
The flag should not normally be switched on because of the degradation in security that results.

Auth/no_check_in_some_cases (version 3.0F onwards -default value depends on release) This parameter needs to be set to ‘Y’ for installation of the profile generator. It defines the use of table USOBT in the authority checks undertaken and allows authority checks to be disabled in individual transactions. Whilst SAP recommends switching off unnecessary authority checks, the full impact of this should be considered carefully.

• Auth/object_disabling_active (default value -‘N’) Whilst_no_check_in_some_cases allows authority checks to be switched off in for individual transactions, this parameter allows checks on individual objects to be switched off globally within SAP. It is recommended that this parameter is not set.

Number of Authorisations in User Buffers

• Auth/auth_number_in_userbuffer When a user logs onto SAP, the authorizations contained in the user’s profiles are copied to a user buffer in memory. The maximum number of authorizations copied is set by this parameter. The size of the buffer must always exceed the maximum number of authorizations as authorization checks are made only against those in the buffer. The default value is 800, but this can be set to between 1–2000. Refer to OSS notes 84209 and 75908 for more detailed information regarding changes to the size of the user buffer.
Transaction SU56 shows the contents of the user’s user buffer and a total for all the authorizations in a user master record.

Table, ABAP and RFC system parameters

• Rec/client (default value - ‘N’) The parameter switches automatic table logging on. Images of the table before and after are logged rather than just changes and so consideration to which tables are to be logged and log volumes must be made before using this as part of a control solution.

• Auth/rfc_authority_check (default value - ‘1’)
The parameter determines how object S_RFC is checked during RFC calls. The object has three fields, activity, the name of the function being called and the function group in which the function resides. The parameter defines whether S_RFC object is checked and if so, whether the function group field is included in the validation.

Value = 0, no check against S_RFC

Value = 1, check active but no check for SRFC-FUGR

Value = 2, check active and check against SRFC-FUGR

• Auth/system_access_check_off (default value - ‘0’ - check remains active) This parameter inactivates the automatic authorization check for particular ABAP/4 language elements (file operations, CPIC calls, and calls to kernel functions). This parameter ensures the downward compatibility of the R/3 kernel.

Useful Transactions
• TU02 Shows current parameters for all hosts and gives a history of changes to parameters
• RZ10 Maintain system parameters
• RZ11 View single system parameters and their functional area.
• SU56 Shows all authorizations a user has in their user master record and the total number. This is useful to identify apparent authorization failures caused by user buffer overflow.

Useful Reports
RSPARAM displays all system parameters set and applicable to the system and instance in which it is run. From version 4.0 the RSUSR003 report also shows the settings for some of the critical password parameters. The report also shows identifies whether SAP*, DDIC or CPIC have insecure passwords by comparing value of the encrypted password field with the encrypted values of the standard shipped passwords. It also shows whether the SAP* user master record is absent from any clients.


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