Ostatnio na liście Bugtraq pojawił się ciekawy mail podsumowujący Cross Site Scripting holes – błędy w skryptach stosowanych na różnych stronach www, dzięki którym można dokonywać ciekawych rzeczy. Dokładny opis problemu, który znany jest powszechnie od ponad półtora roku, znajdziecie poniżej. Jako ciekawostkę podam fakt, że wśród wyszczególnionych serwerów, które wciąż są nieco dziurawe, znajdują się m.in. strony Microsoftu, Oracle, Netscape, a nawet Google.

  From security@devitry.com Wed Nov 21 11:25:49 2001  Date: 17 Nov 2001 02:05:53 -0000  From: security@devitry.com  To: bugtraq@securityfocus.com  Subject: Cross Site Scripting holes abound    Mailer: SecurityFocus    :::  Summary  ::::        Over a year and a half since CERT issued   warning on Cross Site Scripting, most dynamic   websites are _still_ not filtering user input.  This   lets remote sites access to write scripts on vunlerable  sites, stealing cookies, performing actions on behalf  of user or modifying look of content on site.  I did a   quick   check of the top 15 sites (and other sites I use) and   found holes in _most_ of them.     :::  Sites Affected :::          http://www.microsoft.com/     http://www.msnbc.com/     http://www.oracle.com/      http://www.about.com/      http://www.doubleclick.net/      http://www.netscape.com/     http://www.paypal.com/     http://www.google.com/     ... many more not listed....     :::  Details ::::        In general, if you can replace any url parameter with  "">"   and you get an alert, the site may be vulnerable.        Samples and details listed at     http://www.devitry.com/security.html         The samples on the above site take it one step   futher and send the cookie data to another site.          Even https sites are vulnerable since cookie data  is available to javascript on page.    ::::  Fix  :::::       You should validate or filter all user input, including  hidden form fields and id's passed in url's before  the data is written out to the page.  Any poorly   written script on your whole domain could give you   problems.  (even old ones that do nothing like   testenv)  Filtering or encoding is should be done   for  ", >, < and sometimes '       You should monitor for "script" passed in url's to   your site... However, blocking in the url alone  is not good enough as the parameter could be passed  in "POST" data.       For sites that have your data, you should always   log out at the end of your session, and you should  not surf more then one site at a time.     :::  Discussion :::       Most of these holes were discovered in a matter of   minutes.  It takes more time just to find out the owner  of the site and explain to them why this is a problem.   Is there anyway to fix this on a more global basis?      While these types of holes are not instantly mass  exploitable, it is good (or bad, depending on how you   look at it)  for targeting specify users and sites to   steal sessions and personal info.      -Dave deVitry     security@devitry.com     ps. microsoft.com exploit url withheld because they    think they are safer that way.     pps. all websites involved were contacted, but most  had no timely reply.  

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