Transcript Puppetnets-presentat..

Puppetnets: Misusing Web
Browsers as a Distributed Attack
Infrastructure
Lam Vin The, Spiros Antonatos and
Kostas G. Anagnostakis
Adapted by Gary Bramwell
Motivation
• Considerable effort has been put into
detecting current forms of malware
– Viruses, worms, botnets, …
• Threats as we know them today will
eventually die
– Attackers will avoid traditional attacks
• Attacks on the design of applications is the
next step
– It has already started ( XSS worms, SQL injection
attacks)
Spiros Antonatos
A next-generation attack: Puppetnets
• Botnets have served attackers well so far
• Can we have a botnet in a world without
buffer overflows and spyware?
– You can call me puppetnet
• Puppetnets use the bad design of world wide
web to form a limited version of botnets
– No browser or operating system exploits, only
typical HTML pages
Spiros Antonatos
What can puppetnets do?
• Denial of Service attacks
– Flood a victim with requests
• Scan subnets for open ports
– Distributed nmap-like scans
• Propagate attack vectors
– CodeRed-like worms, XSS worms
• Computational attacks
– Calculate MD5 checksums, password
cracking
Spiros Antonatos
What can’t puppetnets do?
• Unable to have total control on a client
machine
– They live and die inside web browsers
• No raw sockets, no keylogging
• Access to file system is denied
• Access of other pages browsed by the
user is denied
Spiros Antonatos
Puppetnets for DoS attacks
To avoid client-side caching
Stealthiness
Stealthiness
Spiros Antonatos
Effectiveness of DoS
• Depends on two factors:
• Web session time. How long a user stays
on a site
– Most users stay several minutes (nearly 10) in a
page
– Data taken from KDDCUP trace, Webtrends and
our personal pages
• Size of puppetnets. How many users visit
concurrently a site
– 90% of sites have nearly up to one thousand
concurrent users
– Maximum value observed was 1 million
– Data from Alexa, ABCE dataset, Webtrends and
Webalizer
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Measuring DoS
•First input: Ingress
bandwidth
consumed by one
puppet vs. RTT
between browser
and server
MaxURL: make requests with 2K URL length
MaxSYN: make normal requests in an excessive
rate
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•Second input:
Capacity distribution
as measured in
“Variability in TCP
round-trip times”
DDoS firepower of 1000 puppets
• We use aliases to trick the browser handle
same destination as different server
– “www.google.com” is not same as
“www.google.com.” for most browsers
• Aliases help us overcome restrictions of
maximum connections per server
Firefox
Explorer
maxSYN 2 aliases
83.97Mbit/s
106.3Mbit/s
maxSYN 3 aliases
137.26Mbit/s
173.28Mbit/s
maxURL 2 aliases
664.74Mbit/s
502.06Mbit/s
maxURL 3 aliases
1053.79Mbit/s
648.33Mbit/s
Spiros Antonatos
Using puppetnets for scanning
• Example: scan the Internet for servers
listening on port 5349
• The idea is to measure time spent to get a
response
• Do a “sandwich” attack
– <IMG SRC=’http://www.attacker.com/cgibin/ping’>
– <IMG SRC=’http://www.targetsite.com:5349’>
– <IMG SRC=’http://www.attacker.com/cgibin/ping’>
• Time between two requests to attacker.com
is the key information needed
Spiros Antonatos
Optimizing scanning
• In the previous example, for each candidate
target we need two requests to malicious
site
– Not scalable, malicious site is finally
DDoSed
• Use onLoad and onError hooks provided by
javascript
– Sandwich as backup solution, in the absence of
javascript
• Measure the time between request and
onLoad/onError trigger
Spiros Antonatos
Scanning illustrated
•We need to define two paramaters: unreachable and timeout
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Defining scanning parameters
• Measured time
to get the main
index of 50,880
web servers
• Measurements
from four
different
network points
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– Geographically
distributed
– Different
connectibity
characteristics
Effectiveness of scanning
• The longer the
timeout is, the
less scans we
can do per
minute
– Unreachable
timeout was set
to 200ms
• Less scans
means less
targets found
Note: browsers impose port restrictions, mainly telnet,POP3 and IMAP
Spiros Antonatos
Malicious computations
• Make puppets to perform malicious computations
– RC5 cracking, MD5 calculations, etc.
• Use javascript or Java applets for computations
• A 1000-node is as fast as a 128-node cluster
Method
MD5 calculations
Javascript
380
Java applet
434K
Java stand-alone
640K
C stand-alone
3.3M
Spiros Antonatos
Other cool stuff
• Spam distribution through puppetnets
– Safari browser allows to connect to any port!
• Weakly designed web services can be
exploited
– Lycos mail uses cookies for login
– Form for sending mail is simple (most services
usually put a hidden id)
– Any puppet that has recently logged in to Lycos
can send spam through user’s account
• We found lycos with 30min search, there are
thousands of services out there
Spiros Antonatos
Defenses (1/3)
• Disable Javascript
– Threat will be reduced but not eliminated
– Browsing experience will be altered significantly
• IDS/IPS signatures
– For example, detect SMTP commands inside a
POST
– Hard for DDoS attacks
– Obfuscation of HTML and javascript prevents
static analysis
Spiros Antonatos
Defenses (2/3)
• Client-side behavioral controls
– Limit number of non-local objects
– 99% of websites access 11 or less foreign
domains, 99.94% less than 20
– Can achieve 10x reduction in DDoS
strength while disrupting 0.1% of
websites
– Can be bypassed if attacker has access to
DNS server
Spiros Antonatos
Defenses (3/3)
• Access Tokens
• Server sends a policy to client that
describes the level of trust for a
specific referrer
• Client implements the policy inside
the browser
• If referrer is not trustworthy, all
requests to victim server will be
stopped at the client side
Spiros Antonatos
Access Tokens illustrated
Spiros Antonatos
Access Token limitations
• Requires implementation on client and
browser side
– Server must issue policies
– Client must be set up to implement
policies
• Requests after first are blocked
– First request still sent and acked
– Severely hampers, but still allows DDoS
Spiros Antonatos
Questions?
Spiros Antonatos
Puppetnets: Misusing Web
Browsers as a Distributed Attack
Infrastructure
Lam Vin The, Spiros Antonatos and
Kostas G. Anagnostakis
To appear in ACM CCS 2006
Backup slides
Spiros Antonatos
Web session times
Spiros Antonatos
Puppetnet size
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