KRACKs Against Wi-Fi Serious But Not End of the World

On October 12, researcher Mathy Vanhoef announced a set of Wi-Fi attacks that he named KRACKs, for key reinstallation attacks. These attack scenarios are against the WPA2 authentication and encryption key establishment portions of the most recent set of protocols. The technique is through key reinstallation.

The attack can potentially allow attackers to send attacker controlled data to your Wi-Fi connected device. In some situations, the attacker can break the built in Wi-Fi protocol’s encryption to reveal users’ Wi-Fi messages to the attacker.

However key reinstallation depends on either working with the inherent timing of a Wi-Fi during a discreet, somewhat rare (in computer terms) exchange or the technique depends upon the attacker forcing the vulnerable exchange through some method (see below for examples). Both of these scenarios take a bit of attacker effort, perhaps more effort than using any one of the existing methods for attacking users over Wi-Fi?

For this reason, while KRACKs Attacks is a serious issue that should be fixed as soon as possible (see below), our collective digital lives probably won’t experience a tectonic shift from Wi-Fi key reinstallation attacks (“KRACKs Attacks”).

Please read on for a technical analysis of the issue.

“… because messages may be lost or dropped, the Access Point (AP) will retransmit message 3 if it did not receive an appropriate response as acknowledgment. As a result, the client may receive message 3 multiple times. Each time it receives this message, it will reinstall the same encryption key, and thereby reset the incremental transmit packet number (nonce) and receive replay counter used by the encryption protocol. We show that an attacker can force these nonce resets by collecting and replaying retransmissions of message 3 of the 4-way handshake. By forcing nonce reuse in this manner, the encryption protocol can be attacked, e.g., packets can be replayed, decrypted, and/or forged.”

–Mathy Vanhoef, “Key Reinstallation Attacks: Forcing Nonce Reuse in WPA2”

The highlighted text above is Vanhoef’s, not mine.

Depending upon which key establishment exchange is attacked, as Vanhoef notes, injection of messages might be the result. But, for some exchanges, decryption might also be possible.

For typical Wi-Fi traffic exchange, AES-CCMP is used between the client (user) and the access point (AP, the Wi-Fi router). Decryption using KRACKs is not thought to be possible. But decryption is not the only thing to worry about.

An attacker might craft a message that contains malware, or at least, a “dropper,” a small program that when run will attempt to install malware. Having received the dropper, even though the message may make no sense to the receiving program, the dropper is still retained in memory or temporary, perhaps even permanent, storage by the receiving computer. The attacker then has to figure out some way to run the dropper—in attack parlance, to detonate the exploit that has been set up through the Wi-Fi message forgery.

“Simplified, against AES-CCMP an adversary can replay and decrypt (but not forge) packets. This makes it possible to hijack TCP streams and inject malicious data into them. Against WPA-TKIP and GCMP the impact is catastrophic: packets can be replayed, decrypted, and forged.“

–Mathy Vanhoef, “Key Reinstallation Attacks: Forcing Nonce Reuse in WPA2”

Packet forgery is worse, as the receiver may consider that the data is legitimate, making it easier for an attacker to have the receiver accept unexpected data items, influencing the course of an exchange and establish a basis upon which to conduct follow-on, next-step exploits.

In my opinion KRACKs are a serious problem to which the wise will wish to respond.

The essential problem with Wi-Fi is that it is free to intercept. Radio waves travel over the air, which, as we all know, is a shared medium. One need not “plug in” to capture Wi-Fi (or any radio-carried) packets. One simply must craft a receiver strong enough to “hear,” that is, receive the transmissions of interest.

But although certainly serious, are KRACKs Attacks the end of the known digital universe? I think not.

First, the attacker has to be present and alert to the four-way, WPA2 handshake. If this has already passed successfully, the attacker’s key reinstallation is no longer possible. The handshake must be interjected at exchange #3, which will require some precision. Or, the attacker must force the key exchange.

One could, I imagine, write an attack that would identify all WPA2 handshake exchanges within range, and inject the attacker’s message #3 to each handshake to deliver some sort of follow-on exploit. This would be a shotgun approach, and might on large, perhaps relatively open networks have potential attacker benefits.[1]

Supplicants (as Wi-Fi clients are called) do not constantly handshake. The handshake interchange takes place upon authentication and reauthentication, and in some networks upon shifting from one AP to another when the client changes location (a “handoff”). These are discreet triggers, not a constant flow of handshake message #3. Johnny or Janie attacker has to be ready and set up in anticipation of message #3. That is, right after message #3 goes by, attacker’s #3 must be sent. Once the completed handshake message #4 goes by, I believe that the attack opportunity closes.

I fear that the timing part might be tricky for the average criminal attacker. It would be much easier to employ readily available Wi-Fi sniffing tools to capture sufficient traffic to allow the attacker to crack weak Wi-Fi passwords.

There are well-understood methods for forcing Wi-Fi authentication (see DEAUTH, below). Since these methods can be used to reveal the password for the network or the user, using one of these may be a more productive attack?

There are other methods for obtaining a Wi-Fi password, as well: the password must be stored somewhere on each connecting device or the user would need to reenter the password upon every connection/reconnection. Any attack that gives attacker access to privileged information kept by any device’s operating system can be used to gain locally stored secrets like Wi-Fi passwords.

Wi-Fi password theft (whether WPA-Enterprise or WPA-Personal) through Wi-Fi deauthentication, “DEAUTH”, has been around for some time; there are numerous tools available to make the attack relatively trivial and straight forward.

Nation-state attackers may have access to banks of supercomputers or massive parallel processing systems that they can apply for rapid password cracking of even complex passwords. A targeted nation-state–sponsored Wi-Fi password-cracking attack is difficult to entirely prevent with today’s technologies. There are likely other adversaries with access to sufficient resources to crack complex passwords in a reasonable amount of time, as well[2].

Obviously, as Vanhoef suggests, as soon as your operating system or Wi-Fi client vendor offers an update to this issue, patch it quickly. Problem, hopefully, solved. Please see https://www.krackattacks.com for updates from security vendors that are working with the discoverer. Question your vendor. If your vendor does not respond, pressure them; that’s my suggestion.

Other actions that organizations can couple with good Wi-Fi hygiene are to use good traffic and event analysis tools, such as modern Security Information Event Management (SIEM) software, network ingress and egress capture for anomaly analysis, and perhaps ingress/egress gateways that prevent many types of attack and forms of traffic.

“One can use VPN, SSH2 tunnels, etc., to ensure some safety from ARP poisoning attacks. Mathy Vanhoef also uses an SSL stripper that depends on badly configured web servers. Make sure your TLS implementation is correct!” – Carric Dooley, Global Lead, Foundstone Consulting Services

Organization Wi-Fi hygiene includes rapidly removing rogue access points, Wi-Fi authentication based upon the organization’s central authentication mechanism (thus don’t employ a WPA password), strong password construction rules, and certificates issued to each Wi-Fi client without which access to Wi-Fi will be denied. Add Wi-Fi event logs to SIEM collection and analysis. Find out whether organization access points generate an event on key reinstallation. This is a fairly rare event. If above-normal events are being generated, your Wi-Fi may be suffering from a KRACK.

None of the foregoing measures will directly prevent key reinstallation attacks. Reasonable security practices do make gaining access to Wi-Fi more difficult, which will prevent or slow other Wi-Fi attacks. Plus, physical security ought to pay attention to anyone sitting in the parking lot with a Wi-Fi antenna pointing at a campus building. But that was just as true before KRACKs were discovered.

For home users, use a complex password on your home Wi-Fi. Make cracking your password difficult. Remember, you usually must enter the password only once for each client device.

Maintain multiple Wi-Fi networks (probably, multiple access points), each with different passwords: one for work or other sensitive use; and another for smart TVs and the like and other potentially vulnerable devices such as Internet of Things devices—isolate those from your network shares, printers, and other sensitive data and trusted devices. Install a third Wi-Fi for your guests. That network should be set up so that each session is isolated from the others; all your guests need is to get to the internet. Each SSID network must have a separate, highly varied password: numbers, lowercase, uppercase, symbols. Make it a long passphrase that resists dictionary attacks.

Wi-Fi routers are a commodity; I do not suggest spending a great deal of money. How much speed do your occasional guests really need? Few Internet connections are as fast as even bottom-tier home Wi-Fi. Most of your visitors probably do not need access to your sensitive data, yes? Should your kids have their own Wi-Fi so that their indiscretions do not become yours?

Multiple Wi-Fi networks will help to slow and perhaps confound KRACKs cybercriminals. “Which network should I focus on?” You increase the reconnaissance the attacker must perform to promulgate a successful attack. Maybe they will move on to simpler home network.

If you happen to notice someone sitting in a car in your neighborhood with an open laptop, be suspicious. If they have what looks like an antenna, maybe let law enforcement know.

Basic digital security practices can perhaps help? For instance, use a VPN even over Wi-Fi. Treat Wi-Fi, particularly, publicly available Wi-Fi as an untrustable network. Be cognizant of where the Wi-Fi exists. WPA2 is vulnerable to decryption, so don’t trust airports, hotels, cafes, anywhere where the implementers and maintainers of the network are unknown.

Users of some Android and Linux clients should be aware that an additional implementation error allows an attacker immediate access to the decryption of client and access point Wi-Fi traffic. Remember, all those smart TVs, smart scales, home automation centers, and thermostats are usually nothing more than specialized versions of Linux. Hence, each may be vulnerable. On the other hand, if these are segregated onto a separate, insecure Wi-Fi, at least attackers will not have readily gained your more sensitive network and devices. While waiting for a patch for your vulnerable Android device, perhaps it makes sense to put it on the untrusted home Wi-Fi as a precaution.

You may have noticed that I did not suggest changing the home Wi-Fi passwords. Doing so will not prevent this attack. Still, the harder your WPA2 password is to crack, the more likely common cybercriminals will move on to easier pickings.

As is often the case in these serious issues, reasonable security practices may help. At the same time, failure to patch quickly leaves one vulnerable for as long as it takes to patch. I try to remember that attackers will become ever more facile with these methods and what they can do with them. They will build tools, which, if these have value, will then become ever more widespread. It is a race between attacker capability and patching. To delay deploying patches is typically a dance with increasing risk of exploitation. In the meantime, the traffic from this attack will be anomalous. Watch for it, if you can.

Many thanks to Carric Dooley from Foundstone Professional Services for his suggestions to complete and round out this analysis as well as for keeping me technically accurate.

Cheers,

/brook

[1] “When a client joins a network, it […] will install this key after receiving message 3 of the 4-way handshake. Once the key is installed, it will be used to encrypt normal data frames using an encryption protocol. However, because messages may be lost or dropped, the Access Point (AP) will retransmit message 3 if it did not receive an appropriate response as acknowledgment. […] Each time it receives this message, it will reinstall the same encryption key, and thereby reset the incremental transmit packet number (nonce) and receive replay counter used by the encryption protocol. We show that an attacker can force these nonce resets by collecting and replaying retransmissions of message 3 of the 4-way handshake. By forcing nonce reuse in this manner, the encryption protocol can be attacked, e.g., packets can be replayed, decrypted, and/or forged.”

[2] Interestingly, my LinkedIn password was among those stolen during the 2011 LinkedIn breach. A research team attempted to crack passwords. After 3 months, they cracked something like 75% of the passwords. However, my highly varied, but merely 6 character password was never cracked. While today’s cracking is factors more sophisticated and rapid, still, a varied non-dictionary password still slows the process down considerably.

Why no “S” in IoT?

My friend, Chris Romeo, a security architect and innovator for whom I have deep respect and from whom I learn a great deal just posted a blog about the lack of security (“S”) in Internet of Things (IoT), “The S In IoT Stands For Security“.

Of course, I agree with Chris about his three problem areas:

  1. Lack of industry knowledge
  2. Developer’s lack of security knowledge and understanding
  3. Time to market pressure, particularly as it exists for startups

I don’t think one can argue with these; in fact, these problems have been and continue to be pervasive, well beyond and before the advent of IoT. Still, I would like to add two more points to Chris’ explanation of the problem space, if I may add to what I hope will be an ongoing and lively conversation within the security industry?

First, IoT products are not just being produced at startups; big players are building IoT, too. Where we place sensors and for what purposes is a universe of different solutions, all the way from moisture sensors in soil (for farming), through networkable household gadgets like light bulbs and thermostats, to the activity monitor on a human’s wrist, to wired up athletes, to the by now famous, mirai botnet camera.

Differing use cases involve varying types and levels (postures) of security. It is a mistake to lump these all together.

When at Intel, I personally reviewed any number of IoT projects that involved significant security involvement, analysis, and implementation. I’m going to guess that most of the major activity monitoring server-side components should have had quite a lot of basic web and cloud security in-built? At least for some products, interaction between the device (IoT sensor) and any intermediary device, like a smart phone or personal computer, has also been given some significant security thought – and it turns out, that this is an area where security has been improving as device capabilities have grown.

It’s hard to make an all out statement on the state of IoT security, though I believe that there are troublesome areas, as Chris points out, most especially for startups. Another problem area continues to be medical devices, which have tended to lag badly because they’ve been produced with more open architectures, as has been presented at security conferences time and again. Then, there’s the Jeep Wrangler remote control hack.

Autonomous autos are going to push the envelop for security, since it’s a nexus between machine learning, big (Big BIG) data, consumer convenience, and physical safety. The companies that put the cars together are generally larger companies, though many of these do not lead in the cyber security space. Naturally, the technology that goes into the cars comes from a plethora of concerns, huge, mid-sized, tiny, and startup. Security consciousness and delivery will be a range from clueful to completely clueless across that range. A repeating problem area for security continues to be complex integrations where differing security postures are pasted together without sufficient thought about how interactions are changing the overall security of the integrated system.

Given the foregoing, I believe that it’s important to qualify IoT somewhat, since context, use case, and semantics/structure matter.

Next, and perhaps more important (save the most important for last?) are the economics of development and delivery. This is highlighted best by the mirai camera: it’s not just startups who have pressure. In the camera manufacturer’s case (as I understand it) they have near zero economic incentive to deliver a secure product. And this is after the mirai attack!

What’s going on here? Importantly, the camaras are still being sold. The access point with a well-known, default password is presumably still on the market, though new cameras may have been remediated. Security people may tear their hair out with an emphatic, “Don’t ever do that!” But, consider the following, please.

  • Product occurs distant (China, in this case) from the consumption of the product
  • Production and use occur within different (vastly different, in this case) legal jurisdictions
  • The incentive is to produce product as cheaply as possible
  • Eventual users do not buy “security” (whatever that means to the customer) from the manufacturer
  • The eventual user buys from manufacturer’s customer or that customer’s customer (multiple entities between consumer and producer)

Where’s the incentive to even consider security in the above picture? I don’t see it.

Instead, I see, as a Korean partner of a company that I once worked for said about acquiring a TCP/IP stack, “Get Internet for free?” – meaning of course, use an open source network stack that could be downloaded from the Internet with no cost.

The economics dictate that, manufacturer download an operating system, usually some Linux variant. Add an working driver, perhaps based upon an existing one? Maybe there’s a configuration thingy tied to a web server that perhaps, came with the Linux. Cheap. Fast. Let’s make some money.

We can try to regulate this up, down, sideways, but I do not believe that this will change much. Big companies will do the right thing, and charge more proportionately. Startups will try to work around the regulations. Companies operating under different jurisdictions or from places where adherence is not well policed or can be bribed away will continue to deliver default passwords to an open source operating system which delivers a host ripe for misuse (which is what mirai turns out to be).

Until we shift the economics of the situation, nothing will change. In the case of mirai, since the consumer of the botnet camera was likely not affected during that attack, she or he will not be applying pressure to the camera manufacturer, either. The manufacturer has little incentive to change; the consumer has little pressure to enforce via buying choices.

By the way, I don’t see consumers becoming more security knowledgeable. Concerned about digital security? Sure. Willing to change the default password on a camera or a wifi router? Many consumers don’t even go that far.

We’re in a bind here; the outlook does not look rosy to me. I open to suggestions.

Thanks, Chris, for furthering this discussion.

cheers,

/brook

“We sell Hammers” – Not Security!

“We sell Hammers” – Not Security!

Several former Home Depot employees said they were not surprised the company had been hacked. They said that over the years, when they sought new software and training, managers came back with the same response: “We sell hammers.

Failure to understand the dependence that we have not just on our obvious digital devices – smart phone, laptop, tablet, fancy fitness bling on your wrist – but also on a matrix of interconnection tying all these devices and billions more together – will land you in the hot seat. For about three billion out of the seven billion people on this planet, we have long since passed the point where we are isolated entities who act alone and in some measure of unconnected global anonymity. For most of us, our lives are not just dependent upon technology itself, but also on the capabilities of innumerable, faceless business entities acting on our behalf.

Consider the following, common, but trivial example.

When I swipe my credit card at the pump to purchase petrol, that transaction passes through any number of computation devices and applications operated by a chain of business entities. The following is a typical scenario (an example flow – but not the only one, of course):

  • The point of sale device1, itself (likely supplied by a point of sale provider)
  • The networking equipment at the station2
  • The station’s Internet provider’s equipment (networking, security, applications – you have no idea!)
  • One or more telecom company’s networking infrastructure across the Internet backbone
  • The point of sale company or their proxy
  • More networking equipment and Internet providers
  • A credit card payment processor
  • More networking equipment and Internet providers
  • The card issuer who must validate the card and agree to pay the transaction for me

And so on…. All just to fill my tank up. It’s seamless and invisible – the communications between entities usually bring up an encrypted tunnel, though the protection offered is not as solid as you may hope – Invisible and seamless, except when the processing is not so invisible, like during a compromise and breach.

Every one of these invisible players has to have good enough security to protect me, and you, if you also use some sort of payment card for your petrol.

Home Depot, and Target before them, (and who knows who’s next?) failed to understand that in order to sell a hammer in the Internet world, you’re participating in this huge web of digital interconnection. Even more so, if you’re large enough, your business network will have become an eco-system of digital entities, many of whose security practices will affect your security posture in fairly profound ways. When 2 (or more) systems connect, each may affect the security posture of the other, sometimes in profound ways.

And there be pirates in them waters, Matey. As I wrote in the introduction to my next book, Securing Systems: Applied security architecture and threat models:

“…as of this writing, we are engaged in a cyber arms race of extraordinary size, composition, complexity, and velocity.”

One of the biggest problems for security practitioners remains that the cyber “arms race” isn’t just between a couple of nation-states. Foremost, the nation-state cyber war has to cross the same digital ocean that we use for our daily lives and digital entertainment. The shared web makes every digital citizen, potential “collateral damage”. But, there are more players than governments.

As can occur in a ground war, virtual “warlords” have private cyber armies marauding for loot, my loot, your loot. Those phishing spam don’t come from your friends, right3? Just trying to categorize the various entities engaged in cyber attacks could generate a couple of fine PhD theses and perhaps even provide years of follow-on papers? The number and varying loyalties of the many players who carry out cyber attacks increases the “size” of the problem, adds to the “composition”, and generates a great deal of “complexity”. It’s enough to make a well-meaning box-store retailer bury its collective head in the virtual sand. Which is precisely what happened to that hammer seller, Home Depot.

But answering the “who” doesn’t complete the picture. There’s the macro “how”, as well4. The Internet seems to suffer the “tragedy of the commons“.

In order to keep the Internet sufficiently interesting with compelling content such that we want to participate, it absolutely must remain neutral in character5. While Internet democracy certainly appears to be quite messy, the very thing that drives the diversity of content on the Internet is its level playing field6.

But leaving the Internet as an open field for all to enjoy means that some will take advantage of the many simply because the “pickings” are too rich to ignore. There is just too much to steal to let those resources lay untouched. And the pirates don’t! People actually do answer those “Nigerian Prince” scam emails. Really, someone does. People do buy those knock-off drugs. For the 3 billion of us who are digitally connected, it’s a dangerous digital day, every single day. Watch what you click!

In short, if you’re reading this on my blog site, you are perhaps an unwitting participant in that “cyber arms race of extraordinary size, composition, complexity, and velocity.” And so is every business that employs modern digital capabilities, whether for payments, or any other task. Failure to understand just how dependent a business is upon this matrix of digital interaction will make one a Target (pun intended). CEO’s, you may want to pay closer attention? Ignoring the current realities could cost you your job, perhaps even your career7!

If you think that you only sell objects and not some level of digital security, I fear that you are likely to be very sadly mistaken?

cheers,

/brook

  1. My friend and former colleague, Lucy McCoy, wrote the communications code in the first generation of gas pump payment terminals. At that time, terminals communicated via modem and phone line. She was a serial communications wiz. I remember the point of sale terminal laid out in her lab area. Lucy has since passed away. She was a brilliant engineer; she gave my code the best quality testing ever.
  2. The transactions have to get from station to payment processing, right? Who runs those cable modems and routers at the station? Could be the Internet provider, or maybe not. I run my own modem/routers/switches at home to which I have full admin access.
  3. I don’t know any spammers, as far as I know? Perhaps I make an unwarranted assumption that you don’t, either?
  4. The “what” and “why” of cyber attack seem pretty clear. Beyond attackers after money, they are after some other advantage: geo-political, business, just causes (pick your favourite or most hated cause), career enhancement, what-have-you. This is all pretty well documented. The security industry seems preoccupied with the “what”, i.e., the technical details of exploits. Again, these technical details seem pretty well documented.
  5. Imagine if your most hated or feared government had control over your Internet use, even the Internet itself, and proceeded to feed you exactly what they wanted you to know and prevented you from any other content. How would you like that?
  6. The richness and depth that is an emergent and continuing quality of the Internet, to me, demonstrates the absolute genius of the originators and early framers of the protocols and design.
  7. Of course, if I had a severance of $15.9 million, maybe I wouldn’t very much mind ending my career?

Heartbleed Exposure, What Is It Really?

Heartbleed Exposure, what is it really?

“Heap allocation patterns make private key exposure unlikely” Neel Mehta, discoverer of HeartBleed” 

In the media, there’s been a lot of discussion about what might be exposed from the heartbleed OpenSSL attack. It is certainly true that very sensitive items can be exposed. And over thousands of test runs, sensitive items like private keying materials and the like have been returned by the heartbleed buffer overread.

A very strong case can be made for doing exactly as industry due diligence suggests. Teams should replace private keys on servers that had been vulnerable, once these are patched. But should every person on the Internet change every password? Let’s examine that problems by digging into the details of exactly how heartbleed works.

First, heartbleed has been characterized as an “overflow” error: “Heartbleed is basically a buffer-overflow vulnerability”. This unfortunately is a poor descriptor and somewhat inaccurate. It may make better media copy, but calling heartbleed an “overflow” is a poor technical description upon which to base a measured response.

Heartbleed is not a classic buffer overflow. No flow control or executable code may be injected via heartbleed. A read of attacker chosen memory locations is not possible, as I will explain, below. A better descriptor of heartbleed is a “buffer over-read”. Unintentionally, some data from memory is returned to the attacker. To be precise, heartbleed is a data leak, not a flow control error.

In order to understand what’s possible to disclose, it’s key to understand program “heap” memory. The heap is an area of memory that programs use to store data. Generally speaking, well-written programs (like OpenSSL) do not to put executable code into heap (that is, data) memory[1]. Because data and execution are separated, the attacker has no way through this vulnerability to execute code. And that is key, as we shall see.

As a program runs, bits of data, large and small, temporary and more or less permanent for the run, are put into the heap[2]. Typically, data are put wherever is convenient at the moment of allocation, depending upon what memory is available.

Memory that’s been deallocated gets reused. If an available piece of memory happens to be larger than a requested size, the new sized piece will be filled with the new data, while adjacent to the new data will remain bits and pieces of whatever was there previously.

In other words, while not entirely random, the heap is filled with bits and pieces of data, a little from here, a little from there, a nice big chunk from this session, with a bit left over from some other session, all helter-skelter amongst each other. The heap is a jumble; taking random bits from the heap may be considered to be like attending a jumble sale.

Now, let’s return to heartbleed. The heartbleed bug returns whatever happens to be on the heap just above the 16 bytes that are required for the TLS heartbeat packet. The attacker may request as much as 64K bytes. That’s a nice big chunk of stuff from the heap; make no mistake about it. Anything might be in there. At the very least, decrypted  data intended for application processing will be returned to the attacker[3]. That’s certainly bad! It breaks the confidentiality supposedly gained through the TLS encryption. But getting a random bit is different than requesting an arbitrary memory location at the discretion of the attacker. And that is a very important statement to hold in mind as we respond to this very serious situation.

An analogy to Heartbleed might be a bit like going fishing. Sometimes, we fish where we can clearly see the fish (mountain streams) or signs of fish (clearer lakes), or with a “fish finder” appliance, that identifies fish  under the surface when the fish aren’t visible.

Heartbleed is a lot more like fishing for fish that are deep in a turbulent lake with no fish finding capability. The fisher is guessing. If she or he guesses correctly, fish for dinner. If not, it’s a long day holding onto the fishing rod.

In the same manner, the attacker, the “fisher” as it were, doesn’t know where the “fish”, the goodies are. The bait (the heartbleed request) is cast upon the “lake” (the program heap) in the hopes that a big fish will “bite” (secret “bytes” will get returned).

The attacker can heartbleed to her or his heart’s content (pun intended). That is, if left undiscovered, an attacker can continuously pound the other side of the connection with heartbleeds, perhaps thousands of times. Which means multiple chunks of memory will be returned to the attacker, as the heap allocates, deallocates, and moves data around.

Lots of different heap chunks will get returned. There will likely also be overlap between the chunks that are returned to the attacker. Somewhere within those memory chunks are likely to be some sensitive data. If the private key for a session happens to be in one of those chunks, it will be exposed to the attacker. If any particular session open through the OpenSSL library happens to a contain a password that had been transmitted, it’s been exposed. It won’t take an engineering genius to do an ASCII dump of returned chunks of memory in order to go poking about to find interesting bits.

Still, and nonetheless, this is hunting for goodies in a bit of a haystack. Some people are quite good at that. Let’s acknowledge that outright. But that’s very different than a directed attack.

And should a wise and prepared security team, making good use of appropriate security tools, notice a heartbleed attack, they will most likely kill the connection before thousands of buffers can be read. Heartbleed over any particular connection is a linear process, one packet retrieved at a time. Retrieving lots of data takes some time. Time to respond. Of course, an unprotected and unaware site could allow many sessions to get opened by an attacker, each linearly heartbled, thus revealing far more of what’s on the heap than a single session might. Wouldn’t you notice such anomalous behaviour?

It’s important to note that the returns in the heartbleed packets are not necessarily tied to the attackers’ session. Again, it’s whatever happens to be on the heap, which will contain parts of other sessions. And any particular heartbleed packet is not necessarily connected to the data in a previous or subsequent packet. Which means that there’s no continuity of session nor any linearity between heartbleed retrievals. All session continuity must be pieced together by the attacker. That’s not rocket science. But it’s also work, perhaps significant work.

I’ll reiterate in closing, that this is a dangerous bug to which we must respond in an orderly fashion.

On the other hand, this bug does not give attackers free reign to go after all the juicy targets that may be available on any host, server, or endpoint that happens to have OpenSSL installed. Whatever happens to be on the heap of the process using the OpenSSL library and that is adjacent to the heartbeat buffer will be returned. And that attack may only occur during a TLS session. Simply including the vulnerable library poses no risk, at all. Many programs make use of OpenSSL for other functionality beyond TLS sessions.

This bug is not the unfettered keys to the kingdom, unless a “key to the kingdom” just happens to be on the heap and happens to get returned in the over-read. What gets returned is entirely due to the distribution of the heap at the moment of that particular heartbeat.

Cheers,

/brook

These assertions have been demonstrated in the lab through numerous runs of the heartbleed attack by a  team who cannot be named here. My thanks to them for confirming this assessment. Sorry for not disclosing.

[1] There are plenty of specialized cases that break this rule. But typically, code doesn’t run from the heap; data goes onto the heap. And generally speaking, programs refrain from executing on the heap because it’s a poor security practice. Let’s make that assumption about OpenSSL (and there’s nothing to indicate that this is NOT true in this case), in order to make clear what’s going on with heartbleed.

[2] The libraries that support programs developed with the major development tools and running on the major operating systems have sophisticated heap management services that are consumed by the running application as it allocates and deallocates memory. While care must be exercised in languages like C/C++, the location of where data end up on the heap is controlled by these low-level services.

[3] That is, intended for the application that is using OpenSSL for TLS services.