FOR OFFICIAL DEPARTMENT OF ENERGY USE ONLY _____________________________________________________ The Computer Incident Advisory Capability ___ __ __ _ ___ / | / \ / \___ __|__ /___\ \___ _____________________________________________________ Information Bulletin March 11, 1991, 1330 PST Number B-18 MVS Security Problem with TSO Reconnect Facility ________________________________________________________________________ PROBLEM: MVS security problem with TSO Reconnect Facility PLATFORM: IBM MVS systems running TSO DAMAGE: Allows unintended reconnect to TSO address space from a different term inal without appropriate terminal check or address space modification SOLUTIONS: IBM is working on a permanent solution, but an interim workaround is to set reconnect time (RECONLIM) to 0 in SYS1.PARMLIB (TSOKEYxx) IMPACT OF WORKAROUND: Disallows the use of the TSO Reconnect Facility for all users _______________________________________________________________________ Critical TSO Reconnect Facility Information CIAC has learned of a potential problem that exists in some IBM MVS systems. This potential problem exists in MVS systems that support TSO (Time Sharing Option) and a security package (e.g., RACF), and also use special groups to grant access to information only at designated locations (terminals). If uncorrected, this problem may allow a user to reconnect to a previous session without resetting the special group information. This may allow someone to bypass a security feature that is designed to limit the access to sensitive files to a particular set of terminals. Note that user IDs and passwords are still required to reconnect a session using the TSO Reconnect Facility. The problem, therefore, cannot result in unauthorized access to systems. IBM is aware of this problem, and is working toward a permanent solution. An interim workaround has been devised. When the RECONLIM parameter in the SYS1.PARMLIB(TSOKEYxx)* file is set to zero, any given TSO session will immediately time-out and not allow the reconnect facility to be activated. This will prevent a user from disconnecting and using the Reconnect Facility to resume the session at a later time. Only the Reconnect Facility address space will be modified. No other address spaces will be affected by this change. For additional information or assistance, please contact CIAC: Tom Longstaff (415) 423-4416 or (FTS) 543-4416, or Call CIAC at (415) 422-8193 or (FTS) 532-8193 or send e-mail to ciac@cheetah.llnl.gov. Send FAX messages to: (415) 423-0913 or (FTS) 543-0913 _____ * - The TSOKEY is delivered from IBM with the version TSOKEY00, but many sites have modified this to be some other number, for example TSOKEY01. The RECONLIM parameter should be modified in the appropriate SYS1.PARMLIB file used during the system IPL (Initial Program Load). Tim Harrington provided information contained in this bulletin. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.