A small and quick introduction to ARP poisoning

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This article won’t be about something new nor something extraordinary for any experienced computer security or even the average hacker, but since I’ve been ask this question quite often by some of my friends, I decided to explain how to sniff passwords from a network.  Moreover, I’m well aware I haven’t been writing anything for a while, and I want to get back to it once all my personal matters are resolved. I’ll concentrate on WEP wireless networks since they are almost certain to be cracked easily. Although those a deprecated, there are still used in many household as the out-of-the-box default configuration, so it’s still pertinent in my opinion. Then I will explain the ARP (Address Resolution Protocol) poisoning attack, which will be used to intercept packets between the target and the Internet.

Attacking the WEP wireless network

Packets in a WEP network are encryted, so in order to sniff packets off from it, you’ll first need to acquire the WEP key. This can be done easily with a wireless network adapter that supports monitor mode and the aircrack suite. For the adapter, I’m using the Linksys  Compact Wireless-G USB adapter, model no WUSB54GC. Plug your adapter into a USB connector and boot up your machine. Once you have booted up, make sure Backtrack or any other distribution has detected your adapter:

ifconfig rausb0 up

and then put the adapter in “Monitor Mode”

iwconfig rausb0 mode monitor

The goal of a WEP attack is to capture as many initialization vectors (IVs) as possible. IVs are random numbers used with a either 64, 128 and 256-bit key to encrypt a stream cipher. Those are used so that two exact same plain text do not produce the same ciphertext. The problem with WEP is that IVs are very short, and on a busy network, the same vectors get reused quickly. The IV is 24 bit long, therefore there are 16 777 216 possibilities1. Moreover, changing the IV for each packet is optional. The keys are also quite short, therefore opening the possibility of finding the key with some brute force calculation. No matter what is they key length, you will just need more packets.

The WEP protocol then use the randomly generated IV, the WEP key and pass it throught the RC4 cipher to produce a keystream. The keystream is then XORed with the plain text stream to produce the cipher text, as shown in the picture below:

WEP Encryption Schema
WEP Encryption Schema (from Wikipedia)

So basically, if you get many packets with the same Ivs, different ciphertext, you can now try to brute-force the WEP key. And to get those packets, you need traffic on the network. Now if there are already some people connected and surfing the web, you can easily capture packets and replay them to get more IVs, otherwise, you need to generate the traffic yourself.

Once you’ve tell airodump to capture IVs, we will use aireplay to generate more traffic, and therefore capture more IVs quickly. If you look at the airodump screen, you’ll see it capturing packets.

Once you have the key, you can finally start the poisoning process. As you have seen, I have not detailed how to crack a WEP network as it is widely described all over the net. You can find find good video tutorials from InfinityExists here and here. The last 2600 issue also had a good article about it.

The ARP poisoning attack

The concept behind this is simple. ARP is the protocol that maintains network devices tables up-to-date by associating an IP address with a MAC address. The problem with ARP is that it doesn’t really care about who answered, it will gladly update the tables from whoever says so. Most of the time, it won’t even ask. So the idea behind the attack, is to send the client an ARP answer saying “hey, I’m the gateway, send stuff to me” and a second ARP answer to the real gateway saying “hey there, I’m this guy, send me his stuff”. Then you just have to relay the packets between the victim and the gateway.Those schemas are more simply to understand:

Schema of an ARP Poisoning Attack
Schema of an ARP Poisoning Attack

In Linux, the rerouting can be done using the following iptables commands:

iptables -t nat -A PREROUTING -i <interface> -p tcp –dport <port> -j REDIRECT –to-port <redirection port>

iptables -t nat -D PREROUTING -i <interface> -p tcp –dport <port> -j REDIRECT –to-port <redirection port>

I’m showing those commands because you can do a lot with those. Many web applications such as some Flash applications use RTMP (Real-time messaging protocol) to control web applications, which run locally.  Flash server send commands to the application using message. Using those commands, you can filter the packets send or receive from the Flash server. Simply use a sniffer first, then locate which packets you wish to drop, alter or whatever.

For example, some sites gives you samples of live music or videos for 30 seconds, then nag you to pay. Using a sniffer, analyze the traffic and find that RTMP Invoke packet that closes the connection with the server. Code a quick proxy that will let all packets go to the flash application except for the connection closing RTMP packet. Then use the commands above to redirect traffic to your proxy.

00 03 0d 4f c0 6d 00 11  20 a8 32 8b 08 00 45 00 …O.m..  .2…E.
00 b2 7e 52 40 00 78 06  d0 a1 50 4d 74 05 43 c1 ..~R@.x. ..PMt.C.
ab 3e 07 8f d0 d8 9b a6  b0 eb ea 61 49 3d 80 18 .>…… …aI=..
fe 4a 76 52 00 00 01 01  08 0a 00 ef a6 d0 02 43 .JvR…. …….C
f4 32 43 00 00 00 00 00  76 14 02 00 0f 63 6c 6f .2C….. v….clo
73 65 43 6f 6e 6e 65 63  74 69 6f 6e 00 00 00 00 seConnec tion….
00 00 00 00 00 05 02 00  57 32 30 38 20 46 72 65 …….. W208 Fre
65 63 68 61 74 20 61 63  74 69 76 69 74 79 20 74 echat ac tivity t
69 6d 65 6f 75 74 2e 20  49 66 20 79 6f 75 20 77 imeout.  If you w
65 72 65 20 61 20 6d 65  6d 62 65 72 2c 20 74 68 ere a me mber, th
65 20 66 72 65 65 20 63  68 61 74 20 77 6f 75 6c e free c hat woul
64 20 6e 6f 74 20 74 69  6d 65 20 6f 75 74 21 20 d not ti me out!

Example of a RTMP Invoke packet to close a connection.

Of course you could just use Ettercap, which does exactly what have been mentioned above. Start Ettercap with the following:

sudo ettercap -G -W 128:p:25AAAAC18DEADDADA433332B65

This will open the graphical interface (-G), that is if you have installed the GTK interface to Ettercap. -W specify to listen for wireless networks and to use a 128-bit key with key found earlier. I don’t know what the p is really for. You can also use the text mode.

Ettercap
Ettercap

Then select Sniffing > Unified Sniffing > select on which interface you want to sniff. Then start the sniffing: File > Start Sniffing. Now let’s specify which targets you wanna sniff. Go to Hosts > Scan for hosts. That will locate the hosts on the current network. Then popup the hosts list, Hosts > Show Hosts List.

Ettercap - Hosts Found on the Network
Ettercap - Hosts Found on the Network

On the list, add the router to target 2 and the hosts you wanna sniff to target 1. Only one step left: MITM > ARP poisoning.  Select Sniff Remote Connections > OK.

Ettercap ARP Poisoining Options
Ettercap ARP Poisoining Options

Then you wait for users to connect to pages like MySpace or Hotmail etc…and Ettercap will find out the sensitive information for you.

See also:

Wireless Networking, Praphul Chandra, Alan Bensky, Ron Olexa, Daniel Mark Dobkin, David A. Lide, Farid Dowla

RFC 826 – Ethernet Address Resolution Protocol, David C. Plummer, November 1982, http://www.faqs.org/rfcs/rfc826.html

Wired Equivalent Protocol, Wikipedia, http://en.wikipedia.org/wiki/Wired_Equivalent_Privacy

Ettercap, http://ettercap.sourceforge.net/

NSA’s new data center in San Antonio

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San Antonio will be hosting the new data center of the National Security Agency reports the San Antonio Current[1]. An old Sony factory on the West Military Drive, near San Antonio’s Loop 410 freeway, will be transformed to accommodate enormous size of data, which will mainly be electronic communications such as phone conversations and emails according to author James Bamford:

“No longer able to store all the intercepted phone calls and e-mail in its secret city, the agency has now built a new data warehouse in San Antonio, Texas.”

This city have been chosen for it’s cheap electricity, provided on an independent power grid since Texas as its own, unconnected to the other states’ grid, making it more reliable.

NSA's Datacenter in San Antonio
NSA's Datacenter in San Antonio

Another factor that played was the location of a similar size Microsoft datacenter a few miles away. This center will be the third largest data center of San Antonio.

As for the Sony plant, it’s made out of two connected buildings, offering offices and research areas and totals around 470 000 square feet[2]. It is expected that 1500 employees will work there initially and may employ up to 4000 personnel.


[1] “The panopticon economy”, Greg M. Schwartz, San Antonio Current, December 3, 2008, http://www.sacurrent.com/news/story.asp?id=69607 (accessed on December 8, 2008)

[2] “NSA Plans San Antonio Data Center”, Rich Miller, Data Center Knowledge, April 19, 2007,  http://www.datacenterknowledge.com/archives/2007/04/19/nsa-plans-san-antonio-data-center/ (accessed on December 8, 2008)

Cyber Espionage : The Triggerfish

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ArsTechnica had some bits of information how the triggerfish has been used to retrieve information from cell phones such as the electronic serial number (ESN), phone numbers and other information without the users’ knowledge and without the help of the telephone providers[1]. It was used back in the 90s by the FBI to track legendary hacker Kevin Mitnick[2].

When cell phones are on, they automatically look for cell sites around them in order to connect to the telephone company network. It will then connect to the one having the strongest signal, as it means a better signal. The triggerfish antenna is a high-powered cell site simulator to which any cell phone near enough will connect, as they will consider it as a normal cell site. Once the mobile registers to the triggerfish and the user wants to make or receive a call, the mobile will send the mobile identification number (MIN), which is actually the phone number, the ESN, cell site data, which contains the channel used and sub-geographical location all the incoming and outgoing data of the caller. It will also contain the outgoing or incoming MIN.  According to the documents released by the ACLU, the triggerfish is able to display the following:

“If the cellular telephone is used to make or receive a call, the screen of the digital analyzer/cell site/simulator/triggerfish would include the cellular telephone number (MIN), the call’s incoming or outgoing status, the telephone number dialled, the cellular telephone’s ESN, the date, time and duration of the call, and the cell site number/sector (location of the cellular telephone when the call was connected)[3]

The same document also writes that this device may be able to intercept the contents of the communication if the option is enabled. It’s important to note that the cell phone must be used to receive or send a call (SMS or web also) in other to for the triggerfish to work, as data about the location of the phone will be send in every data packet send and received by the user. This is how organization can track people using cell phones. Since mobiles always need to find new cell sites as the user moves around, it needs to exchange geographical information with the phone in order to locate the cell sites nearest to the mobile.

As told above, the antenna needs to be stronger than the local cell site in order to pickup the registration of the mobiles. Therefore it needs a lot of power and a high-gain. It also needs equipment such as a digital analyzer in order to make sense of the data intercepted by the triggerfish. And for tracking, it needs to be mounted on a truck to follow the signal of course.

There is a way for everyone to build something almost similar as the triggerfish by using an IMSI catcher. An IMSI catcher can be used to intercept GSM phone calls and use the same tactics as the triggerfish: by simulating a cell site. It will then relay data to a genuine cell site in the area. To do that, the IMSI catcher will need a SIM card and will then appear to the genuine cell site as a mobile phone. In other words, the IMSI catcher acts as a man-in-the-middle between the mobile phone and the genuine cell site.

representing the man-in-the-middle attack using an ISMI catcher
Diagram representing the man-in-the-middle attack using an ISMI catcher(4)

Even if it works in the same way as a triggerfish, the IMSI catcher has some serious drawbacks, among others[5]:

  • “It must be ensured, that the mobile phone of the observed person is in standby mode and the correct network operator is found out. Otherwise, for the Mobile Station, there is no need to log into the simulated Base Station.

  • All mobile phones in the catchment area have no access to the network. Incoming and outgoing calls cannot be patched through for these subscribers.

  • […] Since the network access is handled with the SIM/USIM of the IMSI Catcher, the receiver cannot see the number of the calling party. Of course, this also implicates that the tapped calls are not listed in the itemized bill.

  • The assignment near the Base Station can be difficult, due to the high signal level of the original Base Station.”

IMSI Catchers can be found online. They are sold by Rohde & Schwarz. You could buy the GC128 GSM Communication Unit R&S and apply the firmware to transform it into an ISMI catcher.

See also:

Electronic Surveillance Manual“, U.S Department of Justice, June 2005

IMSI Catcher“, Daehyun Strobel, Chair for Communication Security, Ruhr-Universität Bochum, July 13, 2007


[1] “FOIA docs show feds can lojack mobiles without telco help”, Julian Sanchez, ArsTechnica, November 16, 2008, http://arstechnica.com/news.ars/post/20081116-foia-docs-show-feds-can-lojack-mobiles-without-telco-help.html (accessed on November 18, 2008)

[2] “Computer hacker Kevin Mitnick”, Michael Cooke, Essortment.com, 2002, http://www.essortment.com/all/kevinmitnickco_rmap.htm (accessed on November 18, 2008)

[3] “Electronic Surveillance Book : XIV Cell Site Simulators/Digital Analyzer/Triggerfish”, Electronic Surveillance Unit, Department of Justice, June 2005, p.40

[4] “IMSI Catcher”, Daehyun Strobel, Chair for Communication Security, Ruhr-Universität Bochum, July 13. 2007, p.14

[5] Ibid. p.16

Cybercrime Rose by 9% in Britain

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The BBC reports that cybercrime rose by 9% in Britain[1]. This is according to Online Identity firm Garlik which release its 2008 Cybercrime Report. The report contains interesting statistics. Among others, identity theft drop from 92 000 offenses in 2006 to 84 700, a 8% drop[2]. Financial fraud rose by 24% and is expected to increase for 2008-2009, mainly due to the financial crisis going on. The report cites the leaked letter from the Home Office indicating a possible rise in crime[3]. This is really no surprise.

Always according to the report, the top three stolen documents for identity theft were non-UK passports, utility bills and UK passports[4]. As for financial cybercrimes, losses from UK victims amounted to £535million (1 billion $CAN, 869 millions $US), up 25% from 2006. The reports further states this interesting bit of information:

“… personal details and identity information are traded online with the 15 Research conducted by Garlik’s team of researchers investigating the presence of illegal trading networks on the Internet, number of trading networks more than doubling (from 27 to 57) over the past nine months. In a typical day, around 520 individual information traders are identified with 19,217 traders being identified this year. Of these, around 700 are ‘long term’ traders …[5]

Cybercrime in the UK rose by more than 9% in 2007
Cybercrime in the UK rose by more than 9% in 2007

That’s 57 trading network and around 20 000 traders, which, at least for me, is a big number. But the report doesn’t specify how those traders were identified though. The 700 “long-term” traders are seemed to be identified only with their online alias. Therefore if the “20 000 traders” is counted using aliases, this number might be higher than the actual number of traders.

The reports do not goes into great details on how the criminals get the information, but it does mention Trojans, phishing and SQL injections as a way to retrieve the information. As for the damage caused by these for UK companies, 830 000 companies report a computer-related incident last year. Viruses accounted for 21% of those incidents and are on the decline.

Fortunately, the report also mention lack of data protection from the government but fail to give any number, since it’s outside the scope of the document. But shouldn’t it be considered so? Shouldn’t this be considered as criminal negligence? After all, lost data impact lives and can lead to disaster for the victims of this negligence…

Garlik also describe interesting statistics about online harassment. The complete report can be found here: http://www.garlik.com/static_pdfs/cybercrime_report_2008.pdf


[1] “Cybercrime wave sweeping Britain”, BBC News, October 30, 2008,  http://news.bbc.co.uk/2/hi/technology/7697704.stm (accessed October 30, 2008)

[2] “UK Cybercrime Report 2008”, Stefan Fafinski, Neshan Minassian, Garlik, September 2008, p. 5

[3] “Leaked letter predicts crime rise”, BBC News, September 1, 2008,  http://news.bbc.co.uk/2/hi/uk_news/politics/7591072.stm (accessed on October 30, 2008)

[4] “UK Cybercrime Report 2008”, Stefan Fafinski, Neshan Minassian, Garlik, September 2008, p. 12

[5] Idem, p. 16

Quebec Launches Campaign Against Identity Theft

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Yesterday the ISIQ (Institut de la Sécurité de l’Information du Québec) launched its new campaign to educate citizens computer security and protection of personal information over the Internet. The ISIQ launched a new portal, MonIdentité (in French) containing lots of information for users on how to protect their identity and to identify risks such as phishing, spyware, Trojans and weak passwords. The campaign has been launch by Pierre Arcand, deputy of the Mont-Royal district in Montreal.

“We want the citizens to become their own artisans of their security on the Internet, by adopting a secure behavior.” said M. Pierre Arcand.

The campaign comes amid a declaration from the Chaire de recherche du Canada sur la sécurité, identité et technologie (in French) who reports that in the last 3 years, 314 millions personal files where lost in 976 incidents in Canada and in the United States. Half of them were due to the incompetence of the owning corporation or organization.[1]

This is exactly the kind of initiative we need. Humans are always the weakest link in any security network, therefore educating the population about security is essential. My only fear is that this campaign will largely be ignored by the media and the population, since elections are looming in the province and economic news are still the main topic.

Je Protège Mon Identité - ISIQ Portal
Je Protège Mon Identité - ISIQ Portal

[1] “Pour naviguer sans tracas”, Radio-Canada, October 27, 2008, http://www.radio-canada.ca/nouvelles/societe/2008/10/27/003-securite-informatique.shtml (accessed on October 28, 2008)

Twitter Terrorism

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Today the U.S Army discovered something called Twitter, and realized that, as MySpace, Facebook, Google Earth and many other sites, it could be used by terrorists to plan attacks on landmarks or other targets. Although the Army report admits it has no proofs that Twitter is currently used by individuals for terrorism. The report details many interesting scenarios described in the report:

Scenario 1: Terrorist operative “A” uses Twitter with… a cell phone camera/video function to send back messages, and to receive messages, from the rest of his [group]… Other members of his [group] receive near real time updates (similar to the movement updates that were sent by activists at the RNC) on how, where, and the number of troops that are moving in order to conduct an ambush.

Scenario 2: Terrorist operative “A” has a mobile phone for Tweet messaging and for taking images. Operative “A” also has a separate mobile phone that is actually an explosive device and/or a suicide vest for remote detonation. Terrorist operative “B” has the detonator and a mobile to view “A’s” Tweets and images. This may allow “B” to select the precise moment of remote detonation based on near real time movement and imagery that is being sent by “A.”

Scenario 3: Cyber Terrorist operative “A” finds U.S. [soldier] Smith’s Twitter account. Operative “A” joins Smith’s Tweets and begins to elicit information from Smith. This information is then used for… identity theft, hacking, and/or physical [attacks]. This scenario… has already been discussed for other social networking sites, such as My Space and/or Face Book.[1]

Although this is true, for anyone having a clue about technology, this shouldn’t be any news. Any social networking site offers the opportunity to criminals and terrorists extensive information about someone. This can only by solved by educating people about privacy, and why it’s important. This is especially true for security and military personnel.

See also:

Noah Shachtman, “Spy Fears: Twitter Terrorists, Cell Phone Jihadists”, October 24, 2008, http://blog.wired.com/defense/2008/10/terrorist-cell.html (accessed on October 27, 2008)


[1] “Sample Overview: alQaida-Like Mobile Discussions & Potential Creative Uses” http://blog.wired.com/defense/2008/10/terrorist-cell.html (accessed on October 27, 2008)