FOR OFFICIAL DEPARTMENT OF ENERGY USE ONLY
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             The Computer Incident Advisory Capability
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                         Information Bulletin

March 11, 1991, 1330 PST                                     Number B-18

               MVS Security Problem with TSO Reconnect Facility 
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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
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           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
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* - 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
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that its use would not infringe privately owned rights. Reference
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