10 GOLDEN RULES FOR CODING AUTHORIZATION CHECKS IN ABAP

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Dr. Markus Schumacher
March 18, Heidelberg
SAP Security 2014 – Protecting Your SAP Systems Against Hackers And Industrial Espionage
Ten golden rules for coding authorization checks in ABAP
Andreas Wiegenstein

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© 2014 Virtual Forge GmbH | www.virtualforge.com | All rights reserved.© 2014 Virtual Forge GmbH | www.virtualforge.com | All rights reserved.
Andreas Wiegenstein (Twitter: @codeprofiler)
 Founder of Virtual Forge (Heidelberg), responsible for R&D
 SAP Security Researcher, active since 2003
 Received Credits from SAP for 66 reported 0-day Vulnerabilities
 Speaker at international Conferences
 SAP TechEd (USA & Europe), DSAG (Europe)
 BlackHat (Europe), Hack in the Box (Europe)
 Troopers (Europe), IT Defense (Europe), RSA (USA)
 Co-Author of „Sichere ABAP Programmierung" (SAP Press, 2009)
 Co-Author of "ABAP Best Practices Guideline (DSAG, 2013/2014)
 Created training class WDESA3 (ABAP Security) @ SAP University
My car, my house, my boat, …
I am with

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Authorizations in Custom Code
Ongoing survey, results as of March 12, 2014

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Golden Rule #1
Perform authority checks
General advice
 Check with your business department, if (and which) authorizations
are required in order to execute the business logic you provide.
 As a fallback, analyze code that is similar to your business process for
authorization checks.
 If authority checks are required for your custom business logic, add
them to your code.
On average there are 866 missing authority checks in custom code.

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Golden Rule #1
Perform authority checks (cont’d)
Specific advice
 Don't rely on S_RFC authorizations. They only determine, *if* a function module can be
invoked remotely. They are by no means related to the specific business logic of your
custom code. You don't want users with S_RFC * authorizations to be able to issue
purchase orders or to raise someone's salary. Auditors don't like this either...
 Don't rely on authorization groups assigned to reports. They are usually coarse
grained, as the same authorization group is used for multiple programs. And they are not
necessarily related to the specific business logic of your custom code.
 Always check start authorizations when using CALL TRANSACTION, as no implicit start
authorization check is performed by the kernel.
 Function module AUTHORITY_CHECK_TCODE
 Since 740: CALL TRANSACTION … WITH AUTHORITY-CHECK

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Golden Rule #2
Perform authority checks according to SAP standard functionality
General advice
 Always use functionality based on the ABAP command AUTHORITY-
CHECK in order to perform authorization checks.
(A common bad practice is to base authorizations on usernames.)
On average there are 187 hard-coded username checks in custom code.

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Golden Rule #3
Check the result of an authority check
General advice
 Always check the result of sy-subrc after you perform an
AUTHORITY-CHECK. sy-subrc with value zero means authorization
sufficient.
 Since other ABAP commands also change sy-subrc, make sure to
perform the sy-subrc check *immediately* after the AUTHORITY-
CHECK.
On average there are 13 broken authority checks in custom code.

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Golden Rule #4
Perform authority checks for the user that is actually logged on
General advice
 Only check the authorization of the currently logged on user
(by avoiding the optional parameter FOR USER).
On average there are 2 ‘alias’ authority checks in custom code.

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Golden Rule #5
Always use APIs instead of AUTHORITY-CHECK, if they exist
General advice
 Always use specialized API functions for authorization checks instead of
AUTHORITY-CHECK.
Specific advice
 Use AUTHORITY_CHECK_TCODE instead of S_TCODE
 Use AUTHORITY_CHECK_DATASET instead of S_DATASET / S_PATH
On average there are 92 insufficient authority checks in custom code.

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Golden Rule #6
Declare all fields of the authorization object
General advice
 Always use specialized API functions for authorization checks instead of
AUTHORITY-CHECK.
Specific advice
 Always make sure to specify all fields of the authorization object you check.
 If there are fields you don't want to check, mark them as DUMMY in order to
make your intentions explicit.
No meaningful statistical information available at this time.

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Golden Rule #7
Don't use DUMMY values in important fields
General advice
 Do not use DUMMY values in important authorization fields like 'ACTVT'
On average there are 8 DUMMY authority checks (ACTVT) in custom code.

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Golden Rule #8
Don't program privileging authorization checks
AUTHORITY-CHECK OBJECT 'S_DEVELOP'
ID 'DEVCLASS' FIELD '*'
ID 'OBJTYPE' FIELD 'PROG'
ID 'OBJNAME' FIELD lv_prog
ID 'P_GROUP' DUMMY " Field not required in this context
ID 'ACTVT' FIELD '03'.
IF sy-subrc = 0.
READ REPORT lv_prog INTO lt_code.
ENDIF.
General advice
 Avoid "*" values in authorization fields, as they force administrators to grant
unnecessarily high privileges to users
On average there are 2 privileging authority checks (ACTVT) in custom code.

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Golden Rule #9
Make authorization checks early in your business logic
General advice
 If an authorization check is required for a given business logic, it should be
checked as early as possible

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Golden Rule #10
Perform authorization checks in order to avoid dumps
Specific advice
 Always make sure to test for S_DATASET and S_PATH authorizations before
you open a server-side file.

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Further Information
Blog Post “Ten golden rules for ABAP authorization checks”
https://www.virtualforge.com/en/blog/post/ten_golden_rules_authorizations_en.html

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Twitter: @codeprofiler
Thank you for your attention
Andreas Wiegenstein
CTO

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10 GOLDEN RULES FOR CODING AUTHORIZATION CHECKS IN ABAP

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10 GOLDEN RULES FOR CODING AUTHORIZATION CHECKS IN ABAP