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From: jcm@ORNL-MSR.ARPA (James A. Mullens)
Newsgroups: mod.computers.vax
Subject: Re:  DECnet terminals -> VMS and EDT crashes?
Message-ID: <8610311719.AA20764@ORNL-MSR.ARPA>
Date: Fri, 31-Oct-86 12:19:05 EST
Article-I.D.: ORNL-MSR.8610311719.AA20764
Posted: Fri Oct 31 12:19:05 1986
Date-Received: Mon, 3-Nov-86 20:54:23 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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Approved: info-vax@sri-kl.arpa


I recently reported a problem with DECnet, in which a nonpriveleged user
could crash a VMS 4.2 system.  This could be done over an Ethernet link
from an IBM AT running a DECnet work-alike product called CommUnity.

The problem has now been fixed by the CommUnity people.  I think their
explanation of the problem confirms some rumors about the vulnerability of
VMS -- at least VMS 4.2.  They says that their software was mistakenly
sending the wrong length for a DECnet packet.  They actually claimed that
"the packet length field was set to a negative number".  This was, of course,
a violation of the protocal.  Still, it is amazing that VMS accepted
the length specification and acted on it, committing "computer-cide" in the
process.

Our local DEC sales rep mentioned that the early DECnet DOS releases caused
similar problems.  I can believe this.  It seems that a trivial programming
mistake on the sender's side can cause an crash at the receiving end!

It is encouraging that our VMS 4.4 system did not crash under identical
circumstances, but terminated the EDT job running with an access protection
violation.  This may mean that DEC has already fixed this sort of problem
with the current releases of VMS.  On the other hand, the 4.4 system may
have been saved by trivial differences between the two systems.

As a final note, I have been using CommUnity since I received the fix and I
have not found any more problems with the product.

jim mullens / oak ridge national lab / jcm@ornl-msr.arpa