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Judith J. Francis




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Published on: 10 Mar 2017 by francisjud

Online security review: Unstoppable JavaScript Attack Helps Ad Fraud, Tech Support Scams, 0-Day Attacks

Argentinian security expert
Manuel Caballero has published new research that shows how a website owner
could show a constant stream of popups, even after the user has left his site,
or even worse, execute his very own persistent JavaScript code while the user
is on other domains.


There are multiple issues and
attack scenarios that Caballero discovered, but fortunately, they only affect
Internet Explorer 11, but not Edge, or browsers from other vendors.


The bad news is that, according
to Net Market Share, IE11 is the
second ranked browser version, with a market share of 10.46%, right behind
Chrome 55, with 37.27%, meaning it still accounts for a large portion of the
online user base, despite its advanced age.


The undying IE popups


In a blog post published
yesterday, the Caballero demonstrated how a developer could create popups that
persist in the browser, even after the user has left the page where the popup's
code was loaded, either by clicking a link or entering a new URL in the
browser's address bar.


According to the veteran
security researcher, there's no limit on how many popups a malicious website owner
could show users after they left his site.


The only way users can stop the
popups is to close the tab and open a new one. Navigating away from the
malicious page in a new tab also prevents the popups from showing up.


Never-ending popups could be used in
tech support scams


In a real-world scenario, this
Internet Explorer issue could be a handy tool in the arsenal of tech support
scammers, shady advertisers, or other scare ware operators.


A user leaving a shady page
could still receive popups peddling all sorts of products and links, even after
he clearly left the previous domain.


Similarly, users that land on
tech support scam websites and find a way to leave the site will still receive
popups afterward.


If the victim navigates to
reputable or neutral sites, such as Google, Wikipedia, Bing, or others, the
constant stream of subsequent popups could convince almost any non-technical
users into thinking their computers have a real problem indeed, and dial the
tech support number to get help cleaning their computer.


An IE user reading a Forbes
article would receive a malicious ad, and start seeing popups about being
infected with a virus. Navigating to one or more new sites in the same tab will
still show the same popups, leading inexperienced users on the same path to
believe their PC might have real issues.


Despite IE security measure, users can't
block popups


Besides discovering a way to
perpetuate popups across different domains, Caballero says another issue could
be used to disable the checkbox at the bottom of the repeating popups, which
normally IE11 allows users to block.



This second issue can be
integrated into the first, allowing malicious website owners to create popups
that span across multiple domains that are impossible to kill using IE's
built-in popup-limiting system.


Popups are simple attacks. Issue can do
even more harm


But popups are only scratching
the attack surface. The real problem here is that Internet Explorer executes
persistent JavaScript code even after users leave a site. The attacker can
replace the popup code with everything he wants.


"Let's say there's a new
zero day and the attacker needs to download 5 megs into the user ['s
browser]," Caballero told Bleeping Computer in a conversation. "How
can he make sure he has time to download the bits? With a persistent script,
the attacker has time for everything."


"With a persistent script
[like this] you can create a network of bots without installing anything to
anyone," the researcher also added.



IE11 issue is a malvertiser's lottery


"For example, imagine a
malvertising campaign that sets this script and then forces users to make
hidden requests to ads," Caballero noted, explaining that a website owner
could use past site visitors for ad fraud.


"[Y]ou [the fake advertiser]
buy cheap inventory and then, keep rotating hidden ads for hours, until the
user [...] closes the tab."


Even worse, the persistent
script issue can be used as a supplement to already existing exploits,
improving their success rate.


No patch available


At the heart of the persistent
script problem is a universal cross-site scripting (UXSS) bug and Same Origin
Policy (SOP) bypass in IE's htmlFile/ActiveXObject component, which Caballero
described in depth two weeks ago, but only recently realized he could use to do
more damage.


There's no fix available for
this issue because the researcher has decided to stop reporting bugs to
Microsoft after they've ignored many of his previous reports.


Caballero has put together a
demo page that shows all his findings. Make sure you access the page through
Internet Explorer 11.


Last December, Caballero found a
way to abuse Edge's Smart Screen security feature to show warnings on
legitimate domains. This issue too, could be abused by tech support operators,
and this too, Caballero didn't report to Microsoft.

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