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TUCoPS :: Web BBS :: etc :: phorum1.htm

Phorum 3.0.7 various holes



Vulnerability

    Phorum

Affected

    Phorum 3.0.7

Description

    There seem to  be a number  of security holes  in Phorum 3.0.7,  a
    popular  web  forum  software  based  on  php3  and  SQL.   JFs of
    !Hispahack documented several security flaws in his writeup at:

        http://hispahack.ccc.de/en/mi020.htm

    Exploits described  include changing  the master  password for the
    Phorum,   viewing   arbitrary   files   on   the   webserver,   an
    authentication  backdoor,  the  ability  to  perform arbitrary SQL
    commands, and  a mail  relay.   Security Bugware  included text on
    page below.

    After the wwwboard.pl  problems, people started  to look for  more
    serious  ways  of  offering  message  boards,  one  of  which   is
    [supposedly] the  widely used  Phorum, which  uses PHP  and an SQL
    backend.   First  of  all,  the  phorum  distribution comes with a
    security.txt file, read through it  as it is good stuff,  not that
    it covers all of the below outlined attacks, but it does a  REALLY
    good job at protecting your vanilla installation.

    However,  the  Phorum  distribution   has  some  holes  open   for
    exploitation.   Below  you  will  find  a  more  or  less detailed
    description of some of these  problems.  This article is  based on
    findings in a Phorum 3.0.7 installation.  Problems could or  could
    not apply to older  versions (not tested).   Test box was a  Linux
    Slackware 4.0, running  Apache 1.3.9 with  the PHP 3.0.12  module.
    Let's get to it...

    Admin.php3
    ==========
    The admin.php3 script is used to manage the master installation as
    well  as  the  forums  you  may  create. It requires a password to
    access  its  functions,  though  a  trick  allows us to change the
    password to anything we want without requiring any authentication:
    e.g. to change the master password to 'flow':

        http://www.example.com/admin.php3?step=4&option=pass&confirm=flow&newPssword=flow

    Once we have access to the administrative functions, it is trivial
    to read any file [the  user running the http server has access to]
    in the server.  Go into the "Master Settings" function and  change
    the "default .langfile name" field to:

        ../../../../../../../../../../../file/to/view

    e.g.:

        ../../../../../../../../../../../etc/passwd

    reload the admin.php3  page and the  file you have  specified will
    be displayed on screen.

    The admin interface allows us to shutdown "Phorum", allowing us to
    specify a file that should be displayed indicating that the forums
    are down.   Whenever it  is down,  Phorum uses  a "Location"  http
    header to redirect the users to the "down" page.  The name of this
    "down" page can  be changed using  the admin page,  as Phorum uses
    a relative  URL by  default, it  is thus  possible to redirect the
    whole phorum to any arbitrary URL.  Go into the "Master  Settings"
    function and change the "down page name" field to:

        http://site.to.redirect.to?

    The question mark is required, as Phorum appends an extension
    (default .php3) to the file name, and we don't need this on our
    redirected server, do we?  Then we just put Phorum down using the
    admin interface and the redirection is in effect.

    Auth.php3
    =========
    Phorum provides  a facility  to restrict  access to  parts of  the
    phorum (posting, reading, whole site...) by means of the auth.php3
    file.   There is  an explicit  backdoor in  the auth.php3  script,
    which  allows  any  user   called  "boogieman"  to  override   the
    authentication  process,  thus  allowing  the  user  access to any
    restricted webpage without a valid password.

    We just  need to  append the  "PHP_AUTH_USER=boogieman" value pair
    to the restricted webpage URL we are tying to access, e.g:

        www.example.com/index.php3?PHP_AUTH_USER=boogieman
        www.example.com/admin.php3?PHP_AUTH_USER=boogieman
        ...

    As we can see, it  is pointless to protect the  admin.php3 scripts
    using the facilities of auth.php3.

    Code.php3
    =========
    The Phorum distribution  comes with a  file that probably  slipped
    out of the  Phorum website and,  I suppose, was  never intended to
    be released in  the distribution.   This file is  code.php3, which
    accepts a parameter.  If the parameter is a filename of the phorum
    directory, its contents will be shamelessly displayed.  The script
    does a good job at checking  that we can't get out of  the current
    directory, so we can only check for any changes the  administrator
    has made to  the source of  the php scripts  [in which case  she's
    probably removed  the code.php3  script], other  files that reside
    on the same directory (for mkdir afraid admins), etc.

        www.example.com/code.php3?file_to_view e.g.
        www.example.com/code.php3?common.inc
        www.example.com/code.php3?index.shtml

    Upgrade.php3
    ============
    We also find  this tiny script,  which is used  to migrate between
    Phorum 1.x and Phorum 3.x installations.  It allows us to  specify
    (without any kind of  authentication) the tables we  want upgraded
    and the destination tables.  Haven't played much with this, but it
    could be possible to mess up the phorum tables.

    Read.php3 (et al.)
    ==================
    Phorum's  strongest  point  is  that   it  uses  an  SQL   backend
    (PostgreSQL or MySQL) to store the posts, which allows it to scale
    pretty well (e.g.  the best linux distribution website phorum  has
    more than 15k posts and it works fine).  The main problem is  that
    Phorum performs nearly no input checking for most of the variables
    the scripts  pass to  SQL queries.   So we  can use  it to run any
    arbitrary SQL command  on the server.   We won't probably  receive
    much output, but we  can still  use  it to CREATe/DROP tables,  do
    INSERTs,  PostGreSQL  COPYs,  etc.  Can't  speak much of the MySQL
    interface, but using PGSQL there's no way [that we can see] to run
    an arbitrary command on the remote server.  For the examples we'll
    use the read.php3 script, but there probably are others that  will
    allow you  to do  the same  sort of  stuff.   So, to  run the  SQL
    command "DROP TABLE x", we will use:

        http://www.example.com/read.php3?num=1&action=3&sSQL=DROP%20TABLE%20x

    To run this command the Phorum needs to have (at least) one active
    Phorum.

    Violation.php3
    ==============
    For completeness, there  is another minor  bug that allows  anyone
    to send e-mail using  the violation.php3 script, without  any kind
    of authentication.  However, bear in mind that the e-mail sent has
    your [proxy] ip and  fqdn in it.   This could perhaps be  used for
    spam?  The syntax will be:

        http://www.example.com/violation.php3?Mod=address@to.spam&ForumName=text_to_sam

Solution

    Max  Vision   documented  the   exploits  and   corresponding  IDS
    signatures in arachNIDS

        http://whitehats.com/

    The IDS reference codes are IDS205 through IDS209.  The  following
    signatures can be used with Snort to detect these queries:

    alert TCP $EXTERNAL any -> $INTERNAL 80 (msg: "IDS205/web-phorum-admin"; content: "admin.php3"; flags: AP;)
    alert TCP $EXTERNAL any -> $INTERNAL 80 (msg: "IDS206/web-phorum-auth"; content: "PHP_AUTH_USER=boogieman"; flags: AP;)
    alert TCP $EXTERNAL any -> $INTERNAL 80 (msg: "IDS207/web-phorum-code"; content: "code.php3"; flags: AP;)
    alert TCP $EXTERNAL any -> $INTERNAL 80 (msg: "IDS208/web-phorum-read"; content: "read.php3"; flags: AP;)
    alert TCP $EXTERNAL any -> $INTERNAL 80 (msg: "IDS209/web-phorum-violation"; content: "violation.php3"; flags: AP;)

    Phorum  version  3.0.8  is  now  out  and addresses these security
    issues.  It is available for download from the phorum website:

        http://www.phorum.org/downloads/phorum308.tar.gz

    Until that, do following:

      1.) Remove the files  you don't need (code.php3,),  and restrict
          the  ones  that   aren't  public  (admin.php3,   stats.php3,
          upgrade.php3).
      2.) PHP has some built-in security features, like the ability to
          restrict the files  you can access  to the ones  inside your
          htdocs directory. Use them.


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