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Re: Denial of Service in WordPress
From: "MustLive" <mustlive () websecurity com ua>
Date: Thu, 27 Jun 2013 23:50:47 +0300

Hello Ryan!

Attack exactly overload web sites presented in endless loop of redirects. As I showed in all cases of Looped DoS 
vulnerabilities in web sites and web applications, which I wrote about during 2008 (when I created this type of 
attacks) - 2013.

Particularly concerning web applications, before WordPress, I wrote about Looped DoS in Power Phlogger (2009), 
OpenX/Openads (2009), MODx (2012). If you don't understand this type of attack, you should asked in previous years. 
Since it's ~5,5 years old attack, since I created in beginning of 2008. And I consider it as a thing which people 
should be aware about (like about XSS and CSRF). So I recommend you to read my 2008's articles on this topic.

First I've described Looped DoS in November 2008 in my Classification of DoS vulnerabilities in web applications 
(http://websecurity.com.ua/2663/) and then in more details in article Looped DoS (http://websecurity.com.ua/2698/). In 
standard case Looped DoS happens when web applications is redirecting on itself (endless redirect). Browsers vendors 
long time ago became fighting with such state - like Mozilla in earlier versions of their Mozilla browser added 
"Redirect Loop Error" warning (the same function later received Firefox). But not Internet Explorer. In beginning of 
2008 I was not using Opera (so can't say in which version they added this protection) and there was no Chrome, and 
among my browsers only Mozilla and Firefox had such protection, but IE was affected. And exactly IE was the most 
popular browser that time, so such attack would be working in most clients.

Besides, as I always noted in my articles, that there can be such clients, like spiders and other bots (with no limits 
on redirects), which can overload looped site (sites) by going such link. Anyway with time there was appeared more 
browsers with "Redirect Loop Error", so later I created two methods of bypassing "redirect limit" in browsers and 
described them in February 2009 in my article Hellfire for redirectors. About them I've mentioned in my last advisory. 
The first one is presented in looped redirector (http://tinyurl.com/hellfire-url), which I made for that article and 
the second method - it's using JS (both redirects or one redirect on JS and one via 301/302), because browsers only 
blocks endless redirects which use only server headers. With using this methods of creating "Redirector hell" the 
attack will work in all browsers.

If standard case Looped DoS (redirecting on itself) is rare, then there are large number of redirectors out there. 
Which can be used also for DoS attacks. So I used them and created attack described in articles Redirectors' hell 
(http://websecurity.com.ua/2670/) and Hellfire for redirectors (http://websecurity.com.ua/2854/). Never translated 
these articles to English. This attacks (between two redirector services and between web site and redirector service) 
allow to create Looped DoS from a redirector at any site, just needed one redirector to have predictable address, like 
in case of TinyURL's custom alias feature. After that in 2009 in my articles "Redirectors: the phantom menace" 
(http://websecurity.com.ua/3495/) and "Attacks via closed redirectors" (http://websecurity.com.ua/3531/) I wrote about 
all possible attacks via open and closed redirectors, including Looped DoS. So all who want could be familiar with this 

This just affects the client though right? 

This DoS only going on client side unlike other types of DoS (see my classification), but issue of web application is 
in allowing Looped DoS state. You see error message very quickly because you are leaving in 2013 (where already many 
browsers protect against simple form of Looped DoS) and using secure browser - use a browser without this protection 
(like IE) and have fun.

From my understanding you'd have to get the user to click on the tinyurl

How the attack must go to benefit the attacker. One way is to give people (with vulnerable browsers) to click the link 
and see endless loop - it'll not give enough overload on target server, since people will quickly close the browser's 
tab/window. Another one is to give that link to crazy bots (like from search engines), who has no limits on redirects - 
it'll endlessly connect to target site/sites and overload them. Even better way is to put iframe which leads to such 
redirector at some sites (the more the better) - it can be ad network with such "fun banner" or hacked web sites with 
added iframe or via persistent XSS hole. While people will be at such sites the browser in background will be 
infinitely sending requests to target site/sites (in case of WP redirectors it will be two sites for the first attack 
with using of tinyurl.com and one site in case of the second attack, which works in all WordPress, including WP 3.5.2). 
The more time people spend on particular page with injected iframe with endless redirect and the more people are 
visiting such sites, the more effect will be. No need to ask people to "participate in DoS attack", their browser will 
be automatically "participating" via Looped DoS attack (just by entering in any way this endless loop).

Best wishes & regards,
Administrator of Websecurity web site
  ----- Original Message ----- 
  From: Ryan Dewhurst 
  To: MustLive 
  Cc: submissions () packetstormsecurity org ; full-disclosure ; 1337 Exploit DataBase 
  Sent: Thursday, June 27, 2013 8:34 PM
  Subject: Re: [Full-disclosure] Denial of Service in WordPress

  This just affects the client though right? So doesn't DoS a WordPress blog, just presents an error message to the 
user if they click on a crafted link. How could this be used in the real world to cause any risk? 

  From my understanding you'd have to get the user to click on the tinyurl, which would then show them a browser 
redirect error? If this is the case, how does this benefit an attacker?

  On Thu, Jun 27, 2013 at 7:28 PM, MustLive <mustlive () websecurity com ua> wrote:

    Hello list!

    These are Denial of Service vulnerabilities WordPress. Which I've disclosed two days ago 

    About XSS vulnerabilities in WordPress, which exist in two redirectors, I wrote last year 
(http://seclists.org/fulldisclosure/2012/Mar/343). About Redirector vulnerabilities in these WP scripts I wrote already 
in 2007 (and made patches for them). The developers fixed redirectors in WP 2.3, so Redirector and XSS attacks are 
possible only in previous versions.

    As I've recently checked, this functionality can be used for conducting DoS attacks. I.e. to make Looped DoS 
vulnerabilities from two redirectors (according to Classification of DoS vulnerabilities in web applications 
(http://websecurity.com.ua/2663/)), by combining web site on WordPress with redirecting service or other site. This 
attack is similar to looping two redirectors, described in my articles Redirectors' hell and Hellfire for redirectors. 
The interesting, that looped redirector (http://tinyurl.com/hellfire-url), which I've made at 5th of February 2009 for 
my article Hellfire for redirectors, is still working.

    Affected products:

    Vulnerable are all versions of WordPress: for easy attack - WP 2.2.3 and previous versions, for harder attack - WP 
3.5.2 and previous versions. The second variant of attack requires Redirector or XSS vulnerability at the same domain, 
as web site on WP.


    Denial of Service (WASC-10):

    It's needed to create Custom alias at tinyurl.com or other redirector service, which will be leading to 
wp-login.php or wp-pass.php with setting alias for redirection.



    Here are examples of these vulnerabilities:



    This attack will work for WordPress < 2.3. At that Mozilla, Firefox, Chrome and Opera will stop endless redirect 
after series of requests, unlike IE.

    To make this attack work in all versions of the engine, including WordPress 3.5.2, it's needed that redirector was 
on the same domain, as web site on WP. For this it can be used any vulnerability, e.g. reflected XSS or persistent XSS 
(at the same domain), for including a script for redirecting to one of these redirectors:





    This attack will work as in WordPress 3.5.2 and previous versions, as it isn't stopping by the browsers (endless 

    Best wishes & regards,
    Administrator of Websecurity web site

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