<epigraph>
  <attribution>Confucius</attribution
  <simpara>
    The superior man understands what is right;
    the inferior man understands what will sell.
  </simpara>
</epigraph>

<simpara>
  On <link linkend="credits">Silvio Cesare</link>'s site is a
  text file named <filename>elf-pv.txt</filename>.
  Complete title is <quote>Unix ELF Parasites And Virus</quote>,
  dated October 1998.
  It gives some background and then describes the gap between
  code and data segment, as illustrated in <xref linkend="readelf">
  (for some strange reason he does not mention that command anywhere).
</simpara>
<para>
  At the end of the text is an uuencoded file
  <filename>unix-linux-pv-src.tgz</filename> containing sources.
  The package is also available as plain
  <filename>vit-src.tgz</filename>.
  This is explained on the first page of
  <ulink url="&http.silvio.cesare;">&http.silvio.cesare;</ulink>:

  <blockquote>
    <para>
      [&hellip;] The name of this virus by curiosity was given by the
      people at
      <ulink url="http://www.f-prot.com/f-prot/">F-Prot</ulink>
      who noticed the virus created a temp file using the letters VIT.
    </para>
  </blockquote>

  In another text he calls the concept
  <quote>the text segment padding virus (padding infection)</quote>.
</para>
<simpara>
  Anyway, the code is hard to read as he started development with 
  a piece of plain C and applied several transformations.
  It seems that he released the stuff the very second it produced results.
</simpara>

<sect2>
  <title>Three years later</title>

  <simpara>
    <ulink url="&http.securiteam.5MP022K5GE;"
      >Remote Shell Trojan: Threat, Origin and Solution</ulink>
    on <ulink url="&http.securiteam;">&http.securiteam;</ulink> is dated
    10/9/2001.
  </simpara>
  <simpara>
    Perhaps they had to cut out all interesting details to protect
    their source. But what I read on that page makes little sense to me.
    Supposedly <ulink url="&http.jargon.script.kiddies"
      >script kiddies</ulink>
    got hold of experimental back door code and planted it on sites they
    had access to. No names, dates, sites or legal consequences given.
    No details on the method used by intruders to gain access.
  </simpara>

  <blockquote>
    <para>
      [&hellip;] From this point, the virus seemed to spread in
      the wild.
    </para>
  </blockquote>

  <simpara>
    Well, how does it spread? There is no reference to a root
    exploit, either local or remote. It is explained that if
    root starts an infected program owned by another user, a virus
    can pollute the whole system. But how many people really do this?
    (a poll on <ulink url="slashdot.org">slashdot.org</ulink>
    might give answer) And the question on how the virus spreads
    to other machines remains.
  </simpara>
  <simpara>
    It is plausible that script kiddies copy root kits
    (including viral back doors) wholesale to cracked machines.
    It is possible to combine a remote exploit with such a virus
    to build a persistent worm, though creative work of this
    extent is by definition out of reach for script kiddies.
    But in both cases the problem is the used exploit,
    not the qualities of the installed back door.
  </simpara>
  <simpara>
    Anyway, the concluding remark is strange:
  </simpara>
  <blockquote>
    <para>
      [&hellip;] Again, it is strongly recommend that anybody running
      Linux run the detector to see if their system is infected.
      Even if they do not expect anything, they can always optionally
      immunize their system. This is the only way we can fight the
      further spread of this virus.
    </para>
  </blockquote>
  <simpara>
    We should make another poll on
    <ulink url="slashdot.org">slashdot.org</ulink>
    about how many people used the detector.
    It must have been all of them. Or is there another explanation
    that the predicted catastrophe did not occur?
  </simpara>
  <simpara>
    Attached to the article is Perl and C code that detects
    and vaccinates against RST. Though I never encountered the culprit,
    seeing the antidote makes me sure it is a variation of Silvio
    Cesare's concept.
  </simpara>
  <simpara>
    I am certain that my
    <link linkend="turn.the.pages">shabby piece of Perl</link>
    would detect RST, if I had a copy (add collecting to my list
    of incompetencies). And that a
    <link linkend="patchEntryAddr">deactivated</link> infection with
    <xref linkend="one.step.closer"> has the same effect as the
    immunizer on that site. 
  </simpara>
  <simpara>
    Anyway, the code is fooled by the improvements made in
    <xref linkend="entry.point">. It checks whether the entry
    point is exactly 4096 from the end of the code segments.
    If not, the executable is considered immune.
  </simpara>

  <programlisting><inlinemediaobject><imageobject><imagedata
    format="linespecific" fileref="../src/rst/01.inc"
  ></imageobject></inlinemediaobject></programlisting>

  <simpara>
    The code also tries to clean infected executables by restoring
    the entry point. I don't trust that part, however:
  </simpara>

  <programlisting><inlinemediaobject><imageobject><imagedata
    format="linespecific" fileref="../src/rst/02.inc"
  ></imageobject></inlinemediaobject></programlisting>

  <simpara>
    I can't see any attempt to verify the retrieved address.
    Silvio Cesare's classic pieces stored the original entry point
    at a non-intuitive address in the middle of infective code.
  </simpara>

</sect2>
<sect2>
  <title>The lighter side</title>

  <simpara>
    Above code contains everything to build an infector.
    Obviously it is written from reverse angle.
    Posted on a HTML page without <sgmltag>&lt;pre&gt;</sgmltag> or
    <sgmltag>&lt;tt&gt;</sgmltag> tags.
    And there are no references to preceding works and authors.
    But these are all inevitable constraints of trojan source code
    (term invented by me, right now). By delivering a good show
    it is possible to trick unsuspicious high-bandwidth sites
    into hosting educational material of the guild.
  </simpara>

</sect2>
<sect2>
  <title>Another three months later</title>

  <simpara>
    <ulink url="&http.newsbytes.02.173408;"
      >New Linux Backdoor Virus Gains Smarts</ulink>
    on <ulink url="&http.newsbytes;">&http.newsbytes;</ulink>
    is dated 05 Jan 2002.
  </simpara>

  <simpara>
    What does the title mean? I feel very illiterate.
    Does it really fit this text?
  </simpara>
  <blockquote>
    <para>
      [&hellip;]
      To date there have been "limited" reports of the new RST variant
      in the wild, according to Eschelbeck. To replicate, the virus
      requires users to run an infected program from an account with
      "root" permissions. Upon execution, the infected program will
      attempt to spread the virus to all ELF files on the local system,
      he said.
    </para>
  </blockquote>
  <simpara>
    If the virus cannot gain root on it's own devices,
    left alone reach other machines, how does it propagate at all?
    If this is just a fancy kind of back door then it must have been
    planted after successful attack. What type of attack?
    What vulnerability? On what distributions?
    Are there updates available?
    What does <ulink url="&http.cert;">&http.cert;</ulink> say about it?
  </simpara>
  <blockquote>
    <para>
      [&hellip;]
      However, Russell said it would be "dead simple" to attach the
      virus to a useful program, such as a tool that exploits a security
      hole, and beguile some users into running it.
    </para>
  </blockquote>
  <simpara>
    The first sentence is really funny. Do they really say that an
    exploit is a useful program? Or does this just mean that
    <quote>Remote Shell Trojan</quote> is not a trojan according
    to <link linkend="what.exactly.is.a.virus">my definition</link>?
  </simpara>
  <simpara>
    To me it summarizes like this: On some cracked machines 
    a new kind of back door was found. Period.
  </simpara>

</sect2>
<sect2>
  <title>The serious side</title>

  <para>
    There is a lot of documentation in the net. 
    For example the
    <ulink url="&http.linuxdoc.security.HOWTO;">Security-HOWTO</ulink>
    tells this in
    <ulink url="&http.linuxdoc.security.HOWTO.10;"
      >10. What To Do During and After a Breakin</ulink>:
    <blockquote>
      <para>
	[&hellip;]
	Re-installation should be considered mandatory upon an
	intruder obtaining root access. 
	[&hellip;]
      </para>
    </blockquote>
  </para>

  <para>
    There is a
    <ulink url="&faq.unix;">Unix-FAQ</ulink>
    which explains trivia like 
    <ulink url="&faq.unix;/part2/section-13.html">What's wrong
      with having '.' in your $PATH?</ulink>
    More specific information is 
    <ulink url="&faqs.org;/computer-security/most-common-qs/preamble.html"
      >the FAQ</ulink> of comp.security.unix and comp.security.misc.
    Another interesting piece is 
    <ulink url="http://www.washington.edu/R870/Security.html"
      >Unix System Security</ulink> which confronts you with
    <blockquote>
      <para>
	The best place to start is by reading articles, such as:
	<itemizedlist>
	  <listitem>
	    <simpara>
	      <ulink url="http://stimpy.cac.washington.edu/~dittrich/R870/cracking_guide.html">Guide to Cracking Unix article</ulink>
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      <ulink url="http://www.cis.ohio-state.edu/hypertext/faq/usenet/computer-security/">Usenet computer-security FAQ files</ulink>
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      <ulink url="http://www.cis.ohio-state.edu/hypertext/faq/usenet/computer-security/compromise-faq/faq.html">Compromise FAQ</ulink>
	    </simpara>
	  </listitem>
	</itemizedlist>
      </para>
    </blockquote>

    Finally we have the
    <ulink url="&faq.suicide.methods;">suicide methods FAQ</ulink>.
  </para>

  <simpara>
    News sites seem to avoid the topic of prevention like the plague.
    For some yet unknown reason readers are given no hint to educate
    themselves, or question the sanity of day-to-day behavior.
    Security incidences are described as act of evil forces beyond
    mortal control. 
    Instead I detect a strange appeal for magic tools that can
    cure disease after contagion (the second article links to
    <ulink url="&http.qualys;">&http.qualys;</ulink>, which even seems
    to sell them).
  </simpara>
  <simpara>
    There might come the time of a completely brain washed user
    base taking incredible risks every day. This could be a major
    opportunity for the folks coding trojans.
    And perhaps, if dumped down customers exert enough pressure
    on vendors, the security concepts implemented today might be
    <ulink url="&http.newsforge.181122"
      >rendered inactive on a default installation</ulink>.
  </simpara>
</sect2>
<sect2 id="another.theory" xreflabel="Another theory">
  <title>Another theory</title>

  <simpara>
    <ulink url="&http.vnunet.1127965;"
      >Rare Linux virus on the loose</ulink>
    on <ulink url="&http.vnunet;">&http.vnunet;</ulink>
    is dated 03-01-2002.
  </simpara>

  <blockquote>
    <para>
      [&hellip;] The researchers warned that the culprit carrying the
      virus is likely to be "some exploit being passed around,
      possibly a Secure Shell one". Linux users are advised not to
      run exploits from unknown sources. [&hellip;]
    </para>
  </blockquote>

  <simpara>
    The article does not back this up with facts.
    But the idea itself is interesting.
  </simpara>
  <simpara>
    One of the strongest obstacles to virus spread is the distribution
    concept of Linux. Typical installation method is a set of CDs
    from a single vendor. Probably a lot of people don't buy the
    disks but copy them. However, it is really difficult to infect
    ISO-9660 images. Even more if the CDs are copied on the fly
    using two drives.
  </simpara>
  <simpara>
    Most other software is downloaded from a specific site.
    Either a central repository like
    <ulink url="&http.sourceforge;">&http.sourceforge;</ulink>
    or registered on a place like
    <ulink url="&http.freshmeat;">&http.freshmeat;</ulink>.
    Should such a download site ever get infected by a virus
    there is just a single place to shut down.
    Some sites are mirrored to share bandwidth demands.
    But most mirrors are set up to automatically take over changes
    on a daily or weekly base.
    So I guess that all <quote>official</quote> sources of
    infected software will dry up fast.
  </simpara>
  <simpara>
    On the other hand 0-day exploits are traded in secrecy.
    From one hand to the other. Without authoritative origin.
    And little incentive to raise public attention.
  </simpara>
  <simpara>
    But then I doubt that <ulink url="&http.jargon.script.kiddies"
      >script kiddies</ulink> called in security consultants after
    infecting their own machines.
    It might be possible that white hat administrators tested such
    an exploit on their own production machines.
    I agree with the citation that this is a stupid thing to do.
    But in that case the administrators would still have the original
    binary they executed. Which would clarify the issue beyond doubt.
    To me <quote>is likely to be</quote> means that someone might
    have installed the virus without knowing it, but on a machine already
    rooted. Big deal.
  </simpara>

</sect2>
