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TUCoPS :: Linux :: Red Hat/Fedora :: man14~1.htm

man 1.5h10 + man 1.5i-4 (RedHat 7.0, 7.1) root elevation



Vulnerability

    man

Affected

    man 1.5h10 + man 1.5i-4 (RedHat 7.0, 7.1)

Description

    zen-parse found following.   This advisory is  also stored,  along
    with the  exploits at  http://generic.labs.pulltheplug.com/zen/ as
    man.txt. This is a bug in the man package, not the man-db package.

    Multiple versions of man are affected.  The version numbers  given
    are RedHat  rpm version  numbers.   Just because  a version is not
    listed here,  it does  not mean  it is  not vulnerable.   The main
    problem, which  allows root  is in  the /usr/sbin/makewhatis file.
    If there is  no checking for  shell metacharacters in  files being
    used as arguments, it is possible there is a problem.

    man-1.5h1
    =========

        man -S `perl -e 'print ":" x 100'` ls

    will cause  a Segmentation  fault error,  due to  incorrect bounds
    checking in the array used to hold the section list.  Stored after
    the tmp_section_list structure are the heads of a couple of linked
    lists, cat_list and man_list, which  holds the names of the  files
    already shown.

    By using a pointer to strcpy() (the last entry in the GOT) as  the
    'next' pointer,  it is  possible to  overwrite the  address of the
    library  function   'strcpy'  with   a  newly   malloc()ed  string
    containing the  name of  the file  just viewed.   The string  will
    then be executed instead of strcpy.

    (strcpy() is used, because it contains a NULL after it in the GOT,
    which looks to man to mean "This is the tail of the linked  list",
    and because it gets called at the appropriate time.)

    Exploiting this gives you gid man.  (Elevation of gid man ->  root
    dealt with after the next section).

    man-1.5i-4
    ==========
    This version does not have the -S problem.  It does how ever  have
    an overflow  in the  handling of  .so (sourced)  man pages.   If a
    manpage has

        .so something

    as the  first line,  ultimate_source() attempts  to find  the file
    refered to by the something.

    If it  is compressed,  it uses  my_popen(), a  wrapped version  of
    popen() that drops privs to  the users, to read the  contents, and
    check  that  file  for  a   .so  line  as  well.   Under   certain
    circumstances the filename will increase in length.

    As there is no checking for  the existance of the file other  than
    the  return  value  from  the  popen()  call,  it  is possible, by
    embedding shell  metacharacters in  the filename  to be  opened to
    trick it into thinking it succeeded.

    The same  commands that  fool it  into thinking  it succeeded  can
    return the next file  to look at name.   This can be done  several
    times, until the overflow has reached the desired point.  (ultname
    is 8192  bytes long,  but due  to the  layout of  the variables in
    memory, it needs an overflow of more than double that in order  to
    affect yhe list structure used  in the previous exploit, which  is
    what zen's exploit does.)

    Successful exploitation will result in gid man.

    /usr/sbin/makewhatis
    ====================

        ...
            function readline() {
                      if (use_zcat) {
                        result = (pipe_cmd | getline);
                        if (result < 0) {
                          print "Pipe error: " pipe_cmd " " ERRNO > "/dev/stderr";
                        }
        ...
                      if (use_zcat) {
                        pipe_cmd = "zcat " filename;
        ...

    Imagine a file called:

        "ls.1.gz;cd ..;cd ..;cd ..;cd ..;cd ..;cd ..;cd tmp;export PATH=.;gimmeroot;echo .1.gz"

    Mimed exploits:

    ---
    Content-Type: application/octet-stream; name="man-15first.gz"
    Content-Transfer-Encoding: base64
    Content-Disposition: inline; filename="man-15first.gz"
    Content-MD5: 98NPzNGrT4P4i5ziGbtb9g==
    
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    -----
    
    ---
    Content-Type: application/octet-stream; name="man-15second.gz"
    Content-Transfer-Encoding: base64
    Content-Disposition: inline; filename="man-15second.gz"
    Content-MD5: 9DkClpUM1IMmIRl5XuBLOw==
    
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    -----

Solution

    For more info:

        http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=19351
        https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=40400
        https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=41805
        https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=42450
        http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=43213


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