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TUCoPS :: Security App Flaws :: sctrl.htm

SurfControl - bypass site blocking feature



Vulnerability

    SurfControl

Affected

    SurfControl

Description

    Franklin Witter  found following.   It appears  that there  is yet
    another way to bypass the site blocking feature of SurfControl for
    MS Proxy.

    He has set  up our rules  to deny access  to anyone attempting  to
    reach sites classified  as Adult/Sexually Explicit,  Hacking, etc.
    That would  mean that  anyone trying  to reach www.blockedsite.com
    would normally be denied access to the site.

    The workaround:
    1. First,  do an  nslookup on  www.blockedsite.com to  get the  IP
       address of the site -- xxx.xxx.xxx.xxx
    2. Next, convert each octet  to an octal number using  the windows
       calculator -- yyy.yyy.yyy.yyy
    3. Insert eight  (8) leading zeros  in the first  and third octets
       and seven (7) leading zeros in the second and fourth octets  --
       00000000yyy.0000000yyy.00000000yyy.0000000yyy
    4. Type the modified octets  into your browser's address bar  and,
       viola!, your are successfully bypassing the SurfControl filter.

    As  far  as  we  know,  this,  or  close  variations  on this (ie,
    0yyy.0yyy.0yyy.0yyy,  or  turning  the  whole  thing  into binary,
    removing the dots,  and reconverting to  decimal, hex, etc.)  work
    on most, if not all web censors/filters.

    Not  only  does  it  let  you  hit  the first page using the octal
    address, but it allows you to surf the entire site.  We tested  it
    on 3 different systems logged in as different users and were  able
    to make multiple visits to the same site.

    Another way to bypass other  URL filtering software is to  convert
    the IP octets into hex using 0xnnn representation.  Some will  let
    you  block  certain  regex's,  some  won't.   If  it  does support
    regex's,  the   actual  regex   will  depend   on  the   different
    combinations  you  can  use  to  represent  the  IP  octets.   For
    example, a combination of hex, octal, and regular decimal:

        0xc0.168.000000001.1

    Running SurfControl  Version 3.0.0.1  people were  able to  get to
    the  same  'blocked'  sites  on  multiple  machine using the octal
    format.   Not  only  that,  but  blank  lines  gets written to the
    real-time  monitor  window.   A   blank  line  for  every   bypass
    connection...

    A URL containing an  IP address is not  canonical for HTTP.   HTTP
    1.1  does  virtual  hosting  via  the  "Host:" header, so multiple
    distinct servers can be on a single IP.  If you restrict based  on
    IP,  you'll  block  access  to  both  http://www.juicysex.com/ and
    http://www.bible-history.org/,  should  they  both  be on the same
    box.  However, one or none of the sites has the be the default for
    requests where the  site isn't specified.   So, if the  default is
    juicysex,  then  the  IP  address  can  be blocked.  If it's bible
    history,  then  you  don't.   The  bypass  only  "works"  if   the
    restricted site is the default.

Solution

    SurfControl  has  confirmed  this  to  be a vulnerability in 3.0.2
    version.  No ETA for a patch has been given at this point.


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