CIAC A-33

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The Computer Incident Advisory

 · 4 years ago

  

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              The Computer Incident Advisory Capability 
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                        Informational Bulletin 

             Virus Propagation in Novelle and Other Networks     
         
September 21, 1990, 1000 PST                               Number A-33 

Problem:  Virus propagation on write-protected file systems  
Types: Many known viruses, most frequently variants of the Jerusalem 
(Israeli) virus  
Platform: MS-DOS computers  
Damage: Files that use software write-protection schemes cannot be 
assumed safe from damage due to virus infection  
Symptoms: Virus infection on write-protected files 
Detection:  VIRHUNT, RESSCAN, CodeSafe, Vi-Spy, IBM Scan, FPROT 
Eradication: VIRHUNT, CodeSafe, FPROT, and others (see text in p. 2 of 
this bulletin for recommended procedures) 

                 Critical Virus Propagation Facts  
  

This bulletin is to warn of a virus threat to networks for MS-DOS 
systems.  File servers (e.g., Novell file servers) use attribute bits 
to perform write protection on files stored on server machines.  Many 
viruses will clear these attribute protection bits before they attempt 
infection, thus circumventing the write protection scheme.  Thus, 
write-protecting a program does not guarantee that the file is not 
infected with the virus. 

The following is a common scenario reported to CIAC:  a floppy infected 
with the Jerusalem-B virus is inserted into a user's PC attached to a 
Novell network.  Once this virus is executed, it resides in the PC's 
memory.  When the user attempts to logon to the file server (running 
the program login.exe), the virus infects this program, even though the 
program is write-protected.  Login.exe is a shared program that is 
executed by each user as s/he connects to the Novell network.  Thus, 
each time a user logs in to the network, his/her machine immediately 
becomes infected with the Jerusalem-B virus.  The network allows the 
Jerusalem-B virus to spread considerably more quickly than if it had 
spread through exchange of floppy disks. 

When someone disinfects a system of PCs or PC clones on a Novell or 
similar file system,   CIAC recommends the following procedures: 

1)      Detect the virus using one of the recommended packages for 
detecting and identifying the virus.  Determine exactly which virus has 
infected the system, and that all virus types have been detected. 
Contact CIAC if you need assistance. 

2)      Deactivate the network connecting the PCs/PC clones together. 
This includes shutting down the file servers and unmounting the 
partitions from the users' PCs/PC clones. 

3)      Disinfect the server machines using an anti-virus package known 
to be effective against the detected virus.  Alternately, reformat the 
server disks and re-install the system from original diskettes, then 
restore the data files from a recent backup.  Do not attempt to restore 
programs (i.e., executable files) from a backup, as this is likely to 
reinfect your system. 

4)      Disinfect each user's PC/PC clone using the same procedure as 
in step 2. 

5)      Verify that the virus does not reside on the file server or any 
user's PC/PC clone. 

6)      Bring the network file system back up. 

For additional information or assistance, please contact CIAC:  

        Tom Longstaff 
        (415) 423-4416 or (FTS) 543-4416 
        FAX:  (415) 423-0913 or (FTS) 543-0913 

 Send e-mail to: 

        ciac@tiger.llnl.gov 

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