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TUCoPS :: Security App Flaws :: nav06.htm

Norton Antivirus for Exchange 1.5 - two major problems

    Norton Antivirus


    Norton Antivirus for Exchange 1.5


    Jim  Rosenberg  found  following.   Norton  Antivirus for Exchange
    (NavExchange),  a  product  of  Symantec,  suffers  from two major
    problems,  with  impact  described  below.   The system tested was
    version  1.5.   The  most  recent  version  is  2.0, which was not
    tested, but based on information from Symantec it is believed  2.0
    is also vulnerable to the same problems.

    1. "Fail-Open" Design
    When  an  inbound  e-mail  message  arrives,  a  separate  service
    (NavExchange) is contacted  to scan messages  for viruses.   Under
    certain circumstances  -- not  entirely clear  -- NavExchange will
    enter a  state in  which it  fails to  properly respond.   When it
    enters this state, messages containing viruses will be transmitted
    through  to   the  addressed   recipent(s),  leaving   the  system
    completely unprotected.  Jim had at least one fairly clear case in
    which  it  apparently  entered  this  state  as  the result of the
    LiveUpdate process.  In other  cases it is suspected it  can enter
    this state as the result  of errors in the scanning  process, e.g.
    2. below.

    When NavExchange has entered  this "fail-open" state, an  incoming
    e-mail message containing a virus  will leave an error message  in
    the Event  Log.   Thus the  NavExchange system  is not  completely
    "dead", and even seems  somehow aware of its  own failure.  It  is
    not clear  that Symantec  has warned  customers of  the urgency of
    acting on these  Event Log messages,  or that they  are completely
    unprotected when this happens.   An example of such a  message (as
    exported by the NT Resource Kit utility DUMPEL) looks like this:

        6/6/2000	4:07:42 AM	1	400	45	NavExchange	N/A	MAIL	80004005h Jim
        Rosenberg\Inbox Automated Virus Check Message

    By contrast, a  "normal" virus detection  Event Log message  looks
    like this:

        6/6/2000	5:53:17 AM	2	384	3	NavExchange	N/A	MAIL	EICAR Test String.68 Jim Rosenberg\Inbox Repaired

    When  NavExchange  has  entered  this  "fail-open"  state  it will
    apparently stay in  this state indefinitely  until the service  is
    stopped and restarted.   Once the service  has been restarted,  it
    appears virus protection is restored.

    2. Buffer Overrun in the NavExchange unzip engine
    Because an e-mail message could  contain an attachment which is  a
    .zip file, and members of the .zip archive might contain  viruses,
    NavExchange  includes  a  component  for  unzipping  files.   This
    component  contains  a  buffer  overrun  when  the .zip attachment
    contains long file names.

    There's  a  vulnerability  in  Eudora  concerning .zip attachments
    with  long  file  names  and  it's  advisory.   An  attachment was
    included  to  illustrate  the  problem.   This attachment caused a
    NavExchange failure, indicating that NavExchange suffers from  the
    same problem.

        The message in question has Message-ID
        <002801bfbe6c$eccd5bd0$0100a8c0@ultor> from Ultor <Ultor@HERT.ORG>, subject:

    By sending  this message  through mail  system we  can, with  100%
    reproduceability,  cause  NavExchange  to  fail.   The  vendor has
    acknowledged   that   this   attachment   "will   take   down  our

    Impacts fall into three grades of severity:
    A) Entry Mechanism for viruses
       A virus "armored"  inside of a  .zip attachment with  long file
       names  is  virtually  guaranteed  to  be  able  to slip through
       NavExchange and reach the recipient.   In this case the  system
       administrator  will  have  an  Event  Log  message  noting  the
       failure, but may not realize the implications.  Many NT systems
       have no method of explicitly notifying the system administrator
       when Event Log messages of a particular kind occur, and  indeed
       the whole Event Log mechanism typically requires dilligence  on
       the  part  of  the  system  administrator  to  scan  these logs
       manually.  Since  such an armored  e-mail message could  arrive
       overnight or on  a weekend, there  is more than  sufficent time
       for the message  to trigger an  infection before the  Event Log
       message is noticed.

    B) A  remote  user  may  be  able  to  disable  virus   protection
       Jim suspects but  cannot prove that  mechanism 2) above  may be
       able to  induce the  fail-open state  1) described  above.   He
       cannot actually cause this to happen.

    C) A remote  user may be  able to compromise  the security of  the
       mail server

    Because  problem  2)  above  is  a  buffer  overrun,  there is the
    potential that a suitably  designed exploit could execute  code as
    the Exchange user.


    Both of  the issues  listed above  are fixed  in NAVMSE  2.1.  The
    actual scanning is now handled  by separate processes that can  be
    monitored for problems.  They can be shutdown and restarted when a
    problem occurs.   Files that  cause scan  problems are  considered
    suspect and are moved to the quarantine.

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