A short statement on the Heartbleed problem and its impact on common Internet users.

2014-04-11 by lucaskauffman. 2 comments

On the 7th of April 2014 a team of security engineers (Riku, Antti and Matti) at Codenomicon and Neel Mehta of Google Security published information on a security issue in OpenSSL. OpenSSL is a piece of software used in the encryption process; it helps you in coding your computer traffic to ensure unauthorized people cannot understand what you are sending from one computer network to another. It is used in many applications: for example if you use on-line banking websites, code such as OpenSSL helps to ensure that your PIN code remains secret.

The information that was released caused great turmoil in the security community, and many panic buttons were pressed because of the wide-spread use of OpenSSL. If you are using a computer and the Internet you might be impacted: people at home just as much as major corporations. OpenSSL is used for example in web, e-mail and VPN servers and even in some security appliances. However, the fact that you have been impacted does not mean you can no longer use your PC or any of its applications. You may be a little more vulnerable, but the end of the world may still be further than you think. First of all some media reported on the “Heartbleed virus”. Heartbleed is in fact not a virus at all. You cannot be infected with it and you cannot protect against being infected. Instead it is an error in the computer programming code for specific OpenSSL versions (not all) which a hacker could potentially use to obtain  information from the server (which could possibly include passwords and encryption keys, along with other random data in the server’s memory) potentially allowing him to break into a system or account.

Luckily, most applications in which OpenSSL is used, rely on more security measures than only OpenSSL. Most banks for instance continuously work to remain abreast of security issues, and have implemented several measures that lower the risk this vulnerability poses. An example of such a protective measure is transaction signing with an off-line card reader or other forms of two –factor authentication. Typically exploiting the vulnerability on its own will not allow an attacker post fraudulent transactions if you are using two-factor authentication or an offline token generator for transaction signing.

So in summary, does the Heartbleed vulnerability affect end-users? Yes, but not dramatically. A lot of the risk to the end-users can be lowered by following common-sense security principles:

  • Regularly change your on-line passwords (as soon as the websites you use let you know they have updated their software, this is worthwhile, but it should be part of your regular activity)
  • Ideally, do not use the same password for two on-line websites or applications
  • Keep the software on your computer up-to-date.
  • Do not perform on-line transactions on a public network (e.g. WiFi hotspots in an airport). Anyone could be trying to listen in.

Security Stack Exchange has a wide range of questions on Heartbleed ranging from detail on how it works to how to explain it to non-technical friends. 

Authors: Ben Van Erck, Lucas Kauffman

QoTW #46: CTRL+ALT+DEL Login – Rationale behind it?

2013-05-10 by roryalsop. 1 comments

CountZero asked this interesting question: Why is CTRL+ALT+DEL required at login on Windows systems?

His perspective was that it adds an extra step before login, so is bad from a usability perspective, so there must be a reason.

This got a lot of attention, but looking at the top answers:

Adnan‘s answer briefly describes the Secure Attention Key – the Windows kernel will only notify the Winlogon process about this key combination, which prevents it being hijacked by an application, malware or some other process.  In this way, when you press Ctrl+Alt+Del, you can be sure that you’re typing your password in the real login form and not some other fake process trying to steal your password. For example, an application which looks exactly like the windows login. An equivalent of this in Linux is Ctrl+Alt+Pause

Polynomial‘s comment on the answer further expands on the history of this notification:

As a side note: when you say it’s “wired”, what that actually means is that Ctrl+Alt+Del is a mapped to a hardware defined interrupt (set in the APIC, a physical chip on your motherboard). The interrupt was, historically, triggered by the BIOS’ keyboard handler routine, but these days it’s less clear cut. The interrupt is mapped to an ISR which is executed at ring0, which triggers the OS’s internal handler for the event. When no ISR for the interrupt is set, it (usually) causes an ACPI power-cycle event, also known as a hard reboot.

ThomasPornin describes an attack which would work if the Secure Attention Key didn’t exist:

You could make an application which goes full-screen, grabs the keyboard, and displays something which looks like the normal login screen, down to the last pixel. You then log on the machine, launch the application, and go away until some unsuspecting victim finds the machine, tries to log on, and gives his username and password to your application. Your application then just has to simulate a blue screen of death, or maybe to actually log the user on, to complete the illusion.

There is also an excellent answer over on ServerFault, which TerryChia linked to in his answer:

The Windows (NT) kernel is designed to reserve the notification of this key combination to a single process: Winlogon. So, as long as the Windows installation itself is working as it should – no third party application can respond to this key combination (if it could, it could present a fake logon window and keylog your password 😉

So there you have it – as long as your OS hasn’t been hacked, CTRL+ALT+DEL protects you.

Liked this question of the week? Interested in reading it or adding an answer? See the question in full. Have questions of a security nature of your own? Security expert and want to help others? Come and join us at security.stackexchange.com.

About the recent DNS Amplification Attack against Spamhaus: Countermeasures and Mitigation

2013-04-15 by lucaskauffman. 1 comments

A few weeks ago the anti-spam provider Spamhaus was hit by one of the biggest denial of service attacks ever seen, producing over 300 gbit in traffic. The technique used to generate most of the traffic was DNS Amplification, a technique which doesn’t require thousands of infected hosts, but exploits misconfigured DNS servers and a serious design flaw in DNS. We will discuss how this works, what it abuses and how Spamhaus was capable of mitigating the attack.

more »

How can you protect yourself from CRIME, BEAST’s successor?

2012-09-10 by roryalsop. 11 comments

For those who haven’t been following Juliano Rizzo and Thai Duong, two researchers who developed the BEAST attack against TLS 1.0/SSL 3.0 in September 2011, they have developed another attack they plan to publish at the Ekoparty conference in Argentina later this month – this time giving them the ability to hijack HTTPS sessions – and this has started people worrying again.

Security Stack Exchange member Kyle Rozendo asked this question:

With the advent of CRIME, BEASTs successor, what is possible protection is available for an individual and / or system owner in order to protect themselves and their users against this new attack on TLS?

And the community expectation was that we wouldn’t get an answer until Rizzo and Duong presented their attack.

However, our highest reputation member, Thomas Pornin delivered this awesome hypothesis, which I will quote here verbatim:

This attack is supposed to be presented in 10 days from now, but my guess is that they use compression.

SSL/TLS optionally supports data compression. In the ClientHello message, the client states the list of compression algorithms that it knows of, and the server responds, in the ServerHello, with the compression algorithm that will be used. Compression algorithms are specified by one-byte identifiers, and TLS 1.2 (RFC 5246) defines only the null compression method (i.e. no compression at all). Other documents specify compression methods, in particular RFC 3749 which defines compression method 1, based on DEFLATE, the LZ77-derivative which is at the core of the GZip format and also modern Zip archives. When compression is used, it is applied on all the transferred data, as a long stream. In particular, when used with HTTPS, compression is applied on all the successive HTTP requests in the stream, header included. DEFLATE works by locating repeated subsequences of bytes.

Suppose that the attacker is some Javascript code which can send arbitrary requests to a target site (e.g. a bank) and runs on the attacked machine; the browser will send these requests with the user’s cookie for that bank — the cookie value that the attacker is after. Also, let’s suppose that the attacker can observe the traffic between the user’s machine and the bank (plausibly, the attacker has access to the same LAN of WiFi hotspot than the victim; or he has hijacked a router somewhere on the path, possibly close to the bank server).

For this example, we suppose that the cookie in each HTTP request looks like this:

> Cookie: secret=7xc89f+94/wa

The attacker knows the “Cookie: secret=” part and wishes to obtain the secret value. So he instructs his Javascript code to issue a request containing in the body the sequence “Cookie: secret=0”. The HTTP request will look like this:

POST / HTTP/1.1 Host: thebankserver.com (…) Cookie: secret=7xc89f+94/wa (…)

Cookie: secret=0

When DEFLATE sees that, it will recognize the repeated “Cookie: secret=” sequence and represent the second instance with a very short token (one which states “previous sequence has length 15 and was located n bytes in the past); DEFLATE will have to emit an extra token for the ‘0’.

The request goes to the server. From the outside, the eavesdropping part of the attacker sees an opaque blob (SSL encrypts the data) but he can see the blob length (with byte granularity when the connection uses RC4; with block ciphers there is a bit of padding, but the attacker can adjust the contents of his requests so that he may phase with block boundaries, so, in practice, the attacker can know the length of the compressed request).

Now, the attacker tries again, with “Cookie: secret=1” in the request body. Then, “Cookie: secret=2”, and so on. All these requests will compress to the same size (almost — there are subtleties with Huffman codes as used in DEFLATE), except the one which contains “Cookie: secret=7”, which compresses better (16 bytes of repeated subsequence instead of 15), and thus will be shorter. The attacker sees that. Therefore, in a few dozen requests, the attacker has guessed the first byte of the secret value.

He then just has to repeat the process (“Cookie: secret=70”, “Cookie: secret=71”, and so on) and obtain, byte by byte, the complete secret.

What I describe above is what I thought of when I read the article, which talks about “information leak” from an “optional feature”. I cannot know for sure that what will be published as the CRIME attack is really based upon compression. However, I do not see how the attack on compression cannot work. Therefore, regardless of whether CRIME turns out to abuse compression or be something completely different, you should turn off compression support from your client (or your server).

Note that I am talking about compression at the SSL level. HTTP also includes optional compression, but this one applies only to the body of the requests and responses, not the header, and thus does not cover the Cookie: header line. HTTP-level compression is fine.

(It is a shame to have to remove SSL compression, because it is very useful to lower bandwidth requirements, especially when a site contains many small pictures or is Ajax-heavy with many small requests, all beginning with extremely similar versions of a mammoth HTTP header. It would be better if the security model of Javascript was fixed to prevent malicious code from sending arbitrary requests to a bank server; I am not sure it is easy, though.)

As bobince commented:

I hope CRIME is this and we don’t have two vulns of this size in play! However, I wouldn’t say that being limited to entity bodies makes HTTP-level compression safe in general… whilst a cookie header is an obvious first choice of attack, there is potentially sensitive material in the body too. eg Imagine sniffing an anti-XSRF token from response body by causing the browser to send fields that get reflected in that response.

It is reassuring that there is a fix, and my recommendation would be for everyone to assess the risk to them of having sessions hijacked and seriously consider disabling SSL compression support.

Exploiting ATMs: a quick overview of recent hacks

2012-08-10 by lucaskauffman. 0 comments

A few weeks ago, Kyle Rozendo asked a question on the IT Security StackExchange about Cracking a PCI terminal using a trojan based on the card. It caught my attention, so I started digging a little deeper into this matter.

There are some difficulties involved in hacking an ATM:

  • Often proprietary software
  • Often custom OS or modified embedded Windows

This means a high level of understanding is necessary, as well as access to ATMs to test on. All of the attacks I’ve dug up had some level of inside information before they were constructed.

2009: Diebold gets targeted by Skimer-A Trojan

One of the first serious hacks I came by was a Trojan found in ATMs in eastern Europe around 2009. As reported by Sophos, the attack was aimed at Diebold Opteva ATMs.

The Trojan was named Skimer-A. It’s main goals were:

  • Steal information (card numbers and PINs)
  • Allow remote access
  • Drop more malware

The hack required physical access to the machine. The perpetrators used social engineering, to persuade stores to allow them physical access to the machine after hours, so they could install the virus. After an analysis of the malware, Diebold concluded the attackers also had to have inside information about the systems. A lot of the functions used to extract information were part of the ATMs operation software, but were never documented. They also knew administrative passwords and unlocked the custom Windows CE version Diebold used as well as misconfiguring its firewall. (This was concluded from the security update by Diebold.)

2010: ATM Jackpotting by Barnaby Jack

In 2010, McAfee security expert, Barnaby Jack presented his “ATM Jackpotting” at Blackhat. He was able, after careful analysis with physical access to a few teller machines, to write a tool that could remotely exploit an ATM and patch it so you can call a custom menu with an access code or remotely start emptying the ATM’s money cassettes (hence Jackpotting).

The attack is aimed at standalone and hole-in-the-wall ATMs. The ATMs often run:

  • ARM/XSCALE processor
  • Windows CE
  • TCP/IP, Dial Up or CDMA wireless
  • Support for SSL
  • 3DES encrypted pin pad

In his research he used 3 different ATMs (he ordered these and got them delivered at home). He started his research by looking at the internal workings and, although there were some security measures in place, once a he had physical access many possibilities started to appear. He started by looking for a way to modify the boot sequence, because the ATM boots into its proprietary software. This means he has to patch the system so he can get access to a shell. He accomplished this by using a JTAG debugger.

Using the JTAG module, he was able to send a break when starting the difference services. After this he could launch a proper shell.

This work was all necessary to reverse engineer the software and develop the actual attacks:

  • Walk up attack by “upgrading” the firmware with a flashcard (this required physical access, and a key to open the machine and access the motherboard – such keys are standard, and easy to find on the Internet).
  • Remote configuration attack, firmware can be upgraded remotely

The latter is the most interesting attack, but there are some security defenses in place that make a bruteforce attack impossible. However Barnaby Jack was able to find a vulnerability in the authentication mechanism which allowed him to log in to the machine. He wrote a tool to do these attacks, named “Dillinger”. Now the problem he faced was how to find the ATMs on the internet.

Whilst ATMs support TCP/IP, about 95% of all ATMs still connect to the internet using Dial Up. This means War Dialing using a VOIP tool like WarVox, makes it possible to go and find ATMs on the net. Most of the ATMs use a proprietary protocol, so once you identify this protocol you know an ATM is listening on the other side and you can go and try to exploit it. Once you have access to the ATM you can spawn a shell and install a rootkit. You will still need to identify where the ATM is physically located so you can go and collect the money. This is done by reading the configuration file (often the address is present on the receipts).

The rootkit to keep access to the teller is called “Scrooge”. It hides itself on the machine. One difficulty is that the kit needs to be modified for almost every version of ATM software that’s running because of different peripherals and non-standard ways to communicate. After installing the kit you can walk up to the ATM and enter a keys equence on the keypad, this brings up a custom menu that allows you to jackpot the ATM (completely empty it) or give you a specific amount of cash. This can also be done remotely.

Barnaby suggests following countermeasures:

  • Better physical locks
  • Executable signing at the kernel level
  • Implement Trusted Environment
  • Put them on a seperate, firewalled network
  • Disable the Remote Management System if you aren’t using it
  • More and better code auditing

You can find the complete presentation on Vimeo.

2012: MWR InfoSecurity reveals chip and PIN vulnerability

Chip and PIN is a system where one can insert his banking or credit card into a small machine and make an electronic payment. In the U.K. there is a government backed initiative to make these as widespread as possible. MWR InfoSecurity, a Basingstoke (U.K.) based security company, revealed a way to attack these terminals with a custom PIN card. The attacks demonstrated at Blackhat 2012:

  • Producing a fake receipt, making a cashier think the payment was successful
  • Infect PIN entry devices to collect card data and harvest these with another rogue card
  • Network and interface attack

Apparently the exploits involved were present in normal computers more than a decade ago, making you wonder why this problem was ignored or went undetected. Especially when Cambridge University researchers warned banks of the lack of security in these type of machines as early as 2010. Issues included unencrypted and unauthenticated communication between terminal and remote administration server, which makes a man in the middle attack dead easy. At the moment of writing there hasn’t appeared any white paper (I’m aware of or had access to). The devices affected were produced by VeriFone.


If we look at the attacks over time, it becomes clear that they can be deployed faster and faster. The hacks still require a high level of knowledge and understanding of these systems, but because there are some really basic security issues like bad code reviewing, unencrypted/unauthenticated communication and bad physical security, the attacks are seemingly easy to deploy. It’s up to the producers of these machines to start securing them. Companies still rely too much on security through obscurity and do not expect an attack because a hacker would need insider information. Previous articles suggest that it’s not extremely hard to get that information.


QotW #26: Malicious QR Code and Mitigation

2012-05-04 by roryalsop. 0 comments

This week’s Question of the Week was asked by Purge back in February.  His concern has been echoed in various publications – the worry that scanning one of the common QR codes you see in magazine adverts and on billboards could cause something malicious to happen as most QR scanners on smartphones take you straight to the URL encoded in the QR image. This isn’t a malicious QR (unless you count linking to a particular genre of music malicious) but how would you know?

logicalscope pointed out that a QR code was simply an encoding, so anything you could put in a URL could be encoded in a QR code. This could include XSS, SQL Injection or any other URL based attack.

handyjohn linked to a brief paper over on http://dl.packetstormsecurity.net/papers/attack/attaging.pdf outlining how QR codes could be used to direct victims to an attack website. An attacker could simply print QR code stickers and place them over existing ones on popular advertising hoardings to fool people into going to a site either with malicious code, or that is a spoof of the expected website which can ask for credentials from the victim.

roryalsop focused on the mitigation, which can be very straightforward: rather than send the browser directly to the website, just display the URL that is encoded in the QR image. This way the user can make a decision whether it is a malicious website or not (within the usual bounds for Internet users.) Admittedly logicalscope’s final point, that the QR decoder application could have a vulnerability is also true, but by adding in a user validation step we can at least improve security.

How about storing this one in your phone as a Security Stack Exchange business card – assuming people trust you enough to scan it.

Liked this question of the week? Interested in reading it or adding an answer? See the question in full. Have questions of a security nature of your own? Security expert and want to help others? Come and join us at security.stackexchange.com.

Tor: Exploiting the weakest link

2012-04-10 by lucaskauffman. 5 comments

Since the birth of the internet, there has been censorship. People have always been looking for ways to anonymously access the internet, either by proxy or VPN, however these still (can) log traffic origin and destination.

Since a few years there have been a few projects to anonymize traffic. One of the more famous ones is Tor (The Onion Router).

How Tor works

Tor uses servers and clients. When you request a webpage from your client, Tor will make an encrypted request to a randomly selected relay server called an Onion router. This Onion router knows who you are. Next thing the router does is ask another Onion router to relay the message. This second Onion router only knows the first Onion router. The second asks a third, the third asks the fourth, etc. No single router knows the complete route, however the client does.

The client can access a database which holds all the relays and if he wants, he can select his own route or a random route is selected. He then gets all the public keys for the route and encrypts his message in reverse order, starting with the public key of the last node, than the one to last node, etc. So the encryption is layered (just like the layers of an onion). However there is also a message for every node that contains the next hop. Now at the exit router the message is decrypted completely and the request for the webpage is made. For the webserver that serves the question, the client’s IP is the IP of the exit node.

The weakest link

So traffic is encrypted multiple times and relayed through different servers. This ensures anonymity. However… everyone can set up a Tor exit node … and everyone that has an exit node, can monitor the traffic.

The weakness in this technology is one we find in other technologies as well, the so called “user”.

A lot of people are concerned about their anonymity and figure they are safe when using Tor. They forget that when using a physical line or an encrypted Wifi AP, The chances of getting a Man in the Middle Attack (MMA) is small.

Now because we can easily host an exit node, we can sniff traffic from people who think they are anonymous, a lot of people in fact. At 20 Mbit (the max speed we allowed Tor to use), we got about 200 different Facebook sessions a day.


Users forget about certain things, like facebook over https. I’ve heard people say “I’ve enabled https on my facebook account, so when I log in, I’m safe.” Well that’s good for them but they forget that often, if you do not explicitly state https for the facebook login page, your password and username is sent PLAIN TEXT over the internet. Facebook doesn’t know you want a secure line before you are logged in.Obviously this goes up for a lot of different sites other than Facebook.

The whole point of Tor is to be anonymous, but users get facebook accounts with often their full name and address on it, and then log in insecurelly.

One could write a script (and we made a proof of concept), that looks for usernames and passwords or hijacks sessions and automatically goes to a facebook like page “I am using Tor to be anonymous”.

I am not saying Tor is unsafe, all we wanted to proof is that people need to think twice before thinking they are anonymous and safe on the internet. There will always be people that want to do malicious stuff. We could have hijacked about 20 accounts in half an hour and revealed people who use Tor or get into their emailboxes. (like Dan Egerstad also prooved in 2007).

Youtube Video

The comments in the clip are in Dutch, but basically we set up a tor node and used tshark to capture traffic. We specified we were interested in http traffic coming/going from Facebook. We then took the session cookie and injected it into our browser which then automatically logs us into Facebook as that user.


Tor is a good anonymity provider, but like all tools, you need to use it in the correct way.

QotW #17: What would one need to do in order to hijack a satellite?

2012-02-04 by ninefingers. 0 comments

Slightly later than officially planned, question of the week number 17, a weekly feature on security stack exchange is a rather unusual but very interesting choice. We’ve featured it by community votes – and because it’s an interesting study of “how to think about security”.

So, without further ado, Security.SE member Incognito asked: What would one need to do in order to hijack a satellite?.

I did warn you! Well, never fear, it turns out our members know exactly how to do it! So without further ado:


In terms of radio communications security, most satellite communications systems are repeaters, accepting communication from the highest strength incoming signal at will. Most satellites then contain a command module to order the satellite to perform certain actions as necessary. Due to the highly custom nature of individual satellites, the commands that are accepted and the security for them is highly variable, so there’s a lot of potential for exploitation. As one of our answerers puts it:

When it comes to satellites, the word general does not apply.

Legal Concerns

As a result of the wide variety of frequencies and power requirements in use, chances are, attempting to send commands to a satellite are likely to violate local radio laws – as such, we do not recommend it (although we find the study of security very interesting, all the same).

Finding and talking to a satellite

Clearly, if you’re going to communicate with a satellite, you need equipment with sufficient power and range. You’ll need to be aware of the carrier frequency, the maximum satellite range, the data rate and satellite transmitter power. The location and altitude of satellites also matters – some are geostationary and as such are always in range, while others orbit and may only be in range for a specific period of time. Directional antennas with tracking motors will help an awful lot if the satellite changes position at all. Our answers provide even more detailed radio advice and links, so if you’re interested in your radio, do have a read!

Taking control of a satellite

There are several means by which you can take control of a satellite:

  1. Direct comms: If you have identified your target satellite, the most obvious method would be to communicate directly with it, sending it the commands you desire. Depending on the satellite you target your options will vary. You’ll need to be aware of the protocol and options available to you.
  2. MITM: One option for hijacking a satellite is to identify its command and control – the ground station – and intercept its communications. If you can afford to rent a small plane and can fly it over the site, possibly allowing you an advantage.

Doing it legally

It may be possible to purchase satellite time, depending on who you ask – and as such it may be possible to legitimately control a satellite, even if only for a brief period!

The expensive way

Many of the answers given focused on the radio communication protocols – however, Security.SE member and former moderator Graham Lee highlighted the physical security of satellites as a major concern – the only problem being the cost of getting into space. If you can, being able to nudge the satellite is enough to deny service by altering the antenna direction – you may be able to exploit it in other ways, whilst you’re up there. Of course, you don’t need to go up there yourself necessarily – a rocket will do the job adequately well and apparently doesn’t even need explosives!


Satellite security is an interesting area with many concerns that has perhaps been overlooked in our focus on the security of online stores and the like. Thankfully, people are looking at the security of communications systems that rely on satellites!

This QotW writeup relied on answers from Jeff Ferland, this.josh and Graham Lee primarily. Thanks to all our answerers on this particular question for providing their insights!

Can you improve on these answers? Feel free to visit the question and provide additional detail!