In the last few years researchers have observed two significant changes in
malicious activity on the Internet [Schneier 2005; Williams and Heiser 2004;
Symantec 2005]. The first is the shift from amateur proof-of-concept attacks
to professional profit-driven criminal activity. The second is the increasing
sophistication of the attacks. Although significant efforts are made towards
addressing the underlying vulnerabilities, it is very likely that attackers will
try to adapt to any security response by discovering new ways of exploiting systems
to their advantage [Nachenberg 1997]. In this arms race, it is important
for security researchers to proactively explore and mitigate new threats before
they materialize.
This article discusses one such threat, for which we have coined the term
puppetnets. Puppetnets rely on Web sites that coerce Web browsers to (unknowingly)
participate in malicious activities. Such activities include distributed
denial-of-service, worm propagation, and reconnaissance probing and can
be engineered to be carried out in stealth, without any observable impact on
an otherwise innocent-looking Web site. Puppetnets exploit the high degree of
flexibility granted to the mechanisms comprising the Web architecture, such
as HTML and JavaScript. In particular, these mechanisms impose few restrictions
on how remote hosts are accessed. A Web site under the control of an attacker
can thereby transform a collection of Web browsers into an impromptu
distributed system that is effectively controlled by the attacker. Puppetnets
expose a deeper problem in the design of the Web. The problem is that the
security model is focused almost exclusively on protecting browsers and their
host environment from malicious Web servers, as well as servers from malicious
browsers. As a result, the model ignores the potential of attacks against
third parties.
Web sites controlling puppetnets could be either legitimate sites that have
been subverted by attackers, malicious “underground” Web sites that can lure
unsuspected users by providing interesting services (such as free Web storage,
illegal downloads, etc.), or Web sites that openly invite users to participate
in vigilante campaigns. We must note however that puppetnet attacks are
different from previous vigilante campaigns against spam and phishing sites
that we are aware of. For instance, the Lycos “Make Love Not Spam” campaign
[TechWeb.com 2004] required users to install a screensaver in order to
attack known spam sites. Although similar campaigns can be orchestrated using
puppetnets, in puppetnets users may not be aware of their participation, or
may be coerced to do so; the attack can be launched stealthily froman innocentlooking
Web page, without requiring any extra software to be installed, or any
other kind of user action.
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