CA-90:09                    CERT Advisory
                          November 8, 1990
			  VAX/VMS Break-ins

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DESCRIPTION:
 
     Several VAX/VMS systems are presently being subjected to
intrusions by a persistent intruder(s).  The intruder utilizes DECnet,
TCP/IP, and/or X25 access paths to gain unauthorized entry into
accounts (privileged and non-privileged).  Once a privileged account
is breached, the intruder disables auditing & accounting and installs
a trojan horse image on the system.  In the most recent attacks, the
intruder has installed the image VMSCRTL.EXE in SYS$LIBRARY.  (Note
that VMSCRTL.EXE is not a vendor-supplied filename.) The command
procedure DECW$INSTALL_LAT.COM is placed in SYS$STARTUP and installs
the image.  Note that these images and command files are sufficiently
camouflaged so as to appear to be valid VMS system files, even upon
close inspection.

     There is no evidence that the intruder is exploiting any system 
vulnerability to gain access to the affected systems.  The  intruder 
uses valid username/password combinations to gain access to accounts.
The intruder most likely obtains these username/password combinations 
by systematically searching through text files on the user disks of 
penetrated systems for clear-text username/password pairs.  These 
username/password combinations are often valid on remote systems, 
which allows the intruder to access them as well.  Once a privileged 
account is accessed, the intruder will use the AUTHORIZE utility to 
detect and exploit dormant accounts (especially dormant privileged 
accounts).  The intruder has also assigned privileges to dormant 
non-privileged accounts.

 
IMPACT: 

Unauthorized users who gain privileged and/or non-privileged system
access might deliberately or inadvertently affect the integrity of
system information and/or affect the integrity of the computing
resource.  
 
 
SOLUTION:

The following steps are recommended for detecting whether systems at
your site have been compromised:

     1.  Search for SYS$LIBRARY:VMSCRTL.EXE and
SYS$STARTUP:DECW$INSTALL.COM.  (This can be done with the following
DCL command: $ DIR device:[*...]/SINCE=date /MODIFIED).  Note that to
call the command procedure which installs the image, the intruder will
utilize SYSMAN to modify SYS$STARTUP:VMS$LAYERED.DAT.  Thus, there
will be an unexplained modification to SYS$STARTUP:VMS$LAYERED.DAT.
This may be the surest indication of an intrusion, since the intruder
could easily change the names and locations of the trojan horse image
and its accompanying command procedure.

     2.  If you discover that auditing or accounting has been disabled
for a period of time, go into AUTHORIZE and ensure that no password or
other changes were made during that time.  Password changes while
auditing and accounting have been disabled may indicate unauthorized
access into your system.


     The following pre-emptive actions are suggested:

     1. DISUSER all dormant accounts, especially dormant privileged
accounts.

     2. Advise all users of the security problems inherent in placing
username/password combinations in text files.  Consider searching your
user disks for such occurrences.

     3. Change all vendor-supplied default passwords (e.g., MAILER,
DECNET, SYSTEM) and make sure all passwords are difficult to guess.

     4. Make sure that all privileged users have only the minimum
privileges that are REQUIRED to perform their current tasks.

     5. Closely monitor all relevant audit trails.

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Computer Emergency Response Team/Coordination Center (CERT/CC)
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
 
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