Category Archives: Security engineering

Bad security, good security, case studies, lessons learned

Security Engineering: Third Edition

I’m writing a third edition of my best-selling book Security Engineering. The chapters will be available online for review and feedback as I write them.

Today I put online a chapter on Who is the Opponent, which draws together what we learned from Snowden and others about the capabilities of state actors, together with what we’ve learned about cybercrime actors as a result of running the Cambridge Cybercrime Centre. Isn’t it odd that almost six years after Snowden, nobody’s tried to pull together what we learned into a coherent summary?

There’s also a chapter on Surveillance or Privacy which looks at policy. What’s the privacy landscape now, and what might we expect from the tussles over data retention, government backdoors and censorship more generally?

There’s also a preface to the third edition.

As the chapters come out for review, they will appear on my book page, so you can give me comment and feedback as I write them. This collaborative authorship approach is inspired by the late David MacKay. I’d suggest you bookmark my book page and come back every couple of weeks for the latest instalment!

Could a gaming app steal your bank PIN?

Have you ever wondered whether one app on your phone could spy on what you’re typing into another? We have. Five years ago we showed that you could use the camera to measure the phone’s motion during typing and use that to recover PINs. Then three years ago we showed that you could use interrupt timing to recover text entered using gesture typing. So what other attacks are possible?

Our latest paper shows that one of the apps on the phone can simply record the sound from its microphones and work out from that what you’ve been typing.

Your phone’s screen can be thought of as a drum – a membrane supported at the edges. It makes slightly different sounds depending on where you tap it. Modern phones and tablets typically have two microphones, so you can also measure the time difference of arrival of the sounds. The upshot is that can recover PIN codes and short words given a few measurements, and in some cases even long and complex words. We evaluate the new attack against previous ones and show that the accuracy is sometimes even better, especially against larger devices such as tablets.

This paper is based on Ilia Shumailov’s MPhil thesis project.

Struck by a Thunderbolt

At the Network and Distributed Systems Security Symposium in San Diego today we’re presenting Thunderclap, which describes a set of new vulnerabilities involving the security of computer peripherals and the open-source research platform used to discover them. This is a joint work with Colin Rothwell, Brett Gutstein, Allison Pearce, Peter Neumann, Simon Moore and Robert Watson.

We look at the security of input/output devices that use the Thunderbolt interface, which is available via USB-C ports in many modern laptops. Our work also covers PCI Express (PCIe) peripherals which are found in desktops and servers.

Such ports offer very privileged, low-level, direct memory access (DMA), which gives peripherals much more privilege than regular USB devices. If no defences are used on the host, an attacker has unrestricted memory access, and can completely take control of a target computer: they can steal passwords, banking logins, encryption keys, browser sessions and private files, and they can also inject malicious software that can run anywhere in the system.

We studied the defences of existing systems in the face of malicious DMA-enabled peripheral devices and found them to be very weak.

The primary defence is a component called the Input-Output Memory Management Unit (IOMMU), which, in principle, can allow devices to access only the memory needed to do their job and nothing else. However, we found existing operating systems do not use the IOMMU effectively.

To begin with, most systems don’t enable the IOMMU at all. Windows 7, Windows 8, and Windows 10 Home and Pro didn’t support the IOMMU. Windows 10 Enterprise can optionally use it, but in a very limited way that leaves most of the system undefended. Linux and FreeBSD do support using the IOMMU, but this support is not enabled by default in most distributions. MacOS is the only OS we studied that uses the IOMMU out of the box.

This state of affairs is not good, and our investigations revealed significant further vulnerabilities even when the IOMMU is enabled.

We built a fake network card that is capable of interacting with the operating system in the same way as a real one, including announcing itself correctly, causing drivers to attach, and sending and receiving network packets. To do this, we extracted a software model of an Intel E1000 from the QEMU full-system emulator and ran it on an FPGA. Because this is a software model, we can easily add malicious behaviour to find and exploit vulnerabilities.

We found the attack surface available to a network card was much richer and more nuanced than was previously thought. By examining the memory it was given access to while sending and receiving packets, our device was able to read traffic from networks that it wasn’t supposed to. This included VPN plaintext and traffic from Unix domain sockets that should never leave the machine.

On MacOS and FreeBSD, our network card was able to start arbitrary programs as the system administrator, and on Linux it had access to sensitive kernel data structures. Additionally, on MacOS devices are not protected from one another, so a network card is allowed to read the display contents and keystrokes from a USB keyboard.

Worst of all, on Linux we could completely bypass the enabled IOMMU, simply by setting a few option fields in the messages that our malicious network card sent.

Such attacks are very plausible in practice. The combination of power, video, and peripheral-device DMA over Thunderbolt 3 ports facilitates the creation of malicious charging stations or displays that function correctly but simultaneously take control of connected machines.

We’ve been collaborating with vendors about these vulnerabilities since 2016, and a number of mitigations have been shipped. We have also been working with vendors, helping them to use our Thunderclap tools to explore this vulnerability space and audit their systems for problems.

MacOS fixed the specific vulnerability we used to get administrator access in macOS 10.12.4 in 2016, although the more general scope of such attacks remain relevant. More recently, new laptops that ship with Windows 10 version 1803 or later have a feature called Kernel DMA Protection for Thunderbolt 3, which at least enables the IOMMU for Thunderbolt devices (but not PCI Express ones). Since this feature requires firmware support, older laptops that were shipped before 1803 remain vulnerable. Recently, Intel committed patches to Linux to enable the IOMMU for Thunderbolt devices, and to disable the ATS feature that allowed our IOMMU bypass. These are part of the Linux kernel 5.0 which is currently in the release process.

One major laptop vendor told us they would like to study these vulnerabilities in more detail before adding Thunderbolt to new product lines.

More generally, since this is a new space of many vulnerabilities, rather than a specific example, we believe all operating systems are vulnerable to similar attacks, and that more substantial design changes will be needed to remedy these problems. We noticed similarities between the vulnerability surface available to malicious peripherals in the face of IOMMU protections and that of the kernel system call interface, long a source of operating system vulnerabilities. The kernel system call interface has been subjected to much scrutiny, security analysis, and code hardening over the years, which must now be applied to the interface between peripherals and the IOMMU.

As well as asking vendors to improve the security of their systems, we advise users to update their systems and to be cautious about attaching unfamiliar USB-C devices to their machines – especially those in public places.

We have placed more background on our work and a list of FAQs on our website, thunderclap.io. There, we have also open sourced the Thunderclap research platform to allow other researchers to reproduce and extend our work, and to aid vendors in performing security evaluation of their products.

Thunderclap: Exploring Vulnerabilities in Operating System IOMMU Protection via DMA from Untrustworthy Peripherals A. Theodore Markettos, Colin Rothwell, Brett F. Gutstein, Allison Pearce, Peter G. Neumann, Simon W. Moore, Robert N. M. Watson. Proceedings of the Network and Distributed Systems Security Symposium (NDSS), 24-27 February 2019, San Diego, USA.

PhD studentship in side-channel security

I can offer a 3.5-year PhD studentship on radio-frequency side-channel security, starting in October 2019, to applicants interested in hardware security, radio communication, and digital signal processing. Due to the funding source, this studentship is restricted to UK nationals, or applicants who have been resident in the UK for the past 10 years. Contact me for details.

Open Source Summit Europe

I am at the 2018 Open Source Summit Europe in Edinburgh where I’ll be speaking about Hyperledger projects. In follow-ups to this post, I’ll live-blog security related talks and workshops.

The first workshop of the summit I attended was a crash course introduction to EdgeX Foundry by Jim White, the organization’s chief architect. EdgeX Foundry is an open source, vendor neutral software framework for IoT edge computing. One of the primary challenges that it faces is the sheer number of protocols and standards that need to be supported in the IoT space, both on the south side (various sensors and actuators) as well as the north side (cloud providers, on-premise servers). To do this, EdgeX uses a microservices based architecture where all components interact via configurable APIs and developers can choose to customize any component. While this architecture does help to alleviate the scaling issue, it raises interesting questions with respect to API security and device management. How do we ensure the integrity of the control and command modules when those modules themselves are federated across multiple third-party-contributed microservices? The team at EdgeX is aware of these issues and is a major theme of focus for their upcoming releases.

Privacy for Tigers

As mobile phone masts went up across the world’s jungles, savannas and mountains, so did poaching. Wildlife crime syndicates can not only coordinate better but can mine growing public data sets, often of geotagged images. Privacy matters for tigers, for snow leopards, for elephants and rhinos – and even for tortoises and sharks. Animal data protection laws, where they exist at all, are oblivious to these new threats, and no-one seems to have started to think seriously about information security.

So we have been doing some work on this, and presented some initial ideas via an invited talk at Usenix Security in August. A video of the talk is now online.

The most serious poaching threats involve insiders: game guards who go over to the dark side, corrupt officials, and (now) the compromise of data and tools assembled for scientific and conservation purposes. Aggregation of data makes things worse; I might not care too much about a single geotagged photo, but a corpus of thousands of such photos tells a poacher where to set his traps. Cool new AI tools for recognising individual animals can make his work even easier. So people developing systems to help in the conservation mission need to start paying attention to computer security. Compartmentation is necessary, but there are hundreds of conservancies and game reserves, many of which are mutually mistrustful; there is no central authority at Fort Meade to manage classifications and clearances. Data sharing is haphazard and poorly understood, and the limits of open data are only now starting to be recognised. What sort of policies do we need to support, and what sort of tools do we need to create?

This is joint work with Tanya Berger-Wolf of Wildbook, one of the wildlife data aggregation sites, which is currently redeveloping its core systems to incorporate and test the ideas we describe. We are also working to spread the word to both conservators and online service firms.

Making sense of the Supermicro motherboard attack

There has been a lot of ‘fog of war’ regarding the alleged implantation of Trojan hardware into Supermicro servers at manufacturing time. Other analyses have cast doubt on the story. But do all the pieces pass the sniff test?

In brief, the allegation is that an implant was added at manufacturing time, attached to the Baseboard Management Controller (BMC). When a desktop computer has a problem, common approaches are to reboot it or to reinstall the operating system. However in a datacenter it isn’t possible to physically walk up to the machine to do these things, so the BMC allows administrators to do them over the network.

Crucially, because the BMC has the ability to install the operating system, it can disrupt the process that boots the operating system – and fetch potentially malicious implant code, maybe even over the Internet.

The Bloomberg Businessweek reports are low on technical details, but they do show two interesting things. The first is a picture of the alleged implant. This shows a 6-pin silicon chip inside a roughly 1mm x 2mm ceramic package – as often used for capacitors and other so-called ‘passive’ components, which are typically overlooked.

The other is an animation highlighting this implant chip on a motherboard. Extracting the images from this animation shows the base image is of a Supermicro B1DRi board. As others have noted, this is mounted in a spare footprint between the BMC chip and a Serial-Peripheral Interface (SPI) flash chip that likely contains the BMC’s firmware. Perhaps the animation is an artist’s concept only, but this is just the right place to compromise the BMC.

SPI is a popular format for firmware flash memories – it’s a relatively simple, relatively slow interface, using only four signal wires. Quad SPI (QSPI), a faster version, uses six wires for faster transmission. The Supermicro board here appears to have a QSPI chip, but also a space for an SPI chip as a manufacturing-time option. The alleged implant is mounted in part of the space where the SPI chip would go. Limited interception or modification of SPI communication is something that a medium complexity digital chip (a basic custom chip, or an off-the-shelf programmable CPLD) could do – but not to a great extent. Six pins is enough to intercept the four SPI wires, plus two power. The packaging of this implant would, however, be completely custom.

What can an implant attached to the SPI wires do? The BMC itself is a computer, running an operating system which is stored in the SPI flash chip. The manual for a MBI-6128R-T2 server containing the B1DRi shows it has an AST2400 BMC chip.

The AST2400 uses a relatively old technology – a single-core 400MHz ARM9 CPU, broadly equivalent to a cellphone from the mid 2000s. Its firmware can come via SPI.

I downloaded the B1DRi BMC firmware from the Supermicro website and did some preliminary disassembly. The AST2400 in this firmware appears to run Linux, which is plausible given it supports complicated peripherals such as PCI Express graphics and USB. (It is not news to many of us working in this field that every system already has a Linux operating system running on an ARM CPU, before power is even applied to the main Intel CPUs — but many others may find this surprising).

It is possible that the implant simply replaces the entire BMC firmware, but there is another way.

In order to start its own Linux, AST2400 boots using the U-Boot bootloader. I noticed one of the options is for the AST2400 to pick up its Linux OS over the network (via TFTP or NFS). If (and it’s a substantial if) this is enabled in the AST2400 bootloader, it would not take a huge amount of modification to the SPI contents to divert the boot path so that the BMC fetched its firmware over the network (and potentially the Internet, subject to outbound firewalls).

Once the BMC operating system is compromised, it can then tamper with the main operating system. An obvious path would be to insert malicious code at boot time, via PCI Option ROMs. However, after such vulnerabilities came to light, defenses have been increased in this area.

But there’s another trick a bad BMC can do — it can simply read and write main memory once the machine is booted. The BMC is well-placed to do this, sitting on the PCI Express interconnect since it implements a basic graphics card. This means it potentially has access to large parts of system memory, and so all the data that might be stored on the server. Since the BMC also has access to the network, it’s feasible to exfiltrate that data over the Internet.

So this raises a critical question: how well is the BMC firmware defended? The BMC firmware download contains raw ARM code, and is exactly 32MiB in size. 32MiB is a common size of an SPI flash chip, and suggests this firmware image is written directly to the SPI flash at manufacture without further processing. Additionally, there’s the OpenBMC open source project which supports the AST2400. From what I can find, installing OpenBMC on the AST2400 does not require any code signing or validation process, and so modifying the firmware (for good or ill) looks quite feasible.

Where does this leave us? There are few facts, and much supposition. However, the following scenario does seem to make sense. Let’s assume an implant was added to the motherboard at manufacture time. This needed modification of both the board design, and the robotic component installation process. It intercepts the SPI lines between the flash and the BMC controller. Unless the implant was designed with a very high technology, it may be enough to simply divert the boot process to fetch firmware over the network (either the Internet or a compromised server in the organisation), and all the complex attacks build from there — possibly using PCI Express and/or the BMC for exfiltration.

If the implant is less sophisticated than others have assumed, it may be feasible to block it by firewalling traffic from the BMC — but I can’t see many current owners of such a board wanting to take that risk.

So, finally, what do we learn? In essence, this story seems to pass the sniff test. But it is likely news to many people that their systems are a lot more complex than they thought, and in that complexity can lurk surprising vulnerabilities.

Dr A. Theodore Markettos is a Senior Research Associate in hardware and platform security at the University of Cambridge, Department of Computer Science and Technology.

How Protocols Evolve

Over the last thirty years or so, we’ve seen security protocols evolving in different ways, at different speeds, and at different levels in the stack. Today’s TLS is much more complex than the early SSL of the mid-1990s; the EMV card-payment protocols we now use at ATMs are much more complex than the ISO 8583 protocols used in the eighties when ATM networking was being developed; and there are similar stories for GSM/3g/4g, SSH and much else.

How do we make sense of all this?

Reconciling Multiple Objectives – Politics or Markets? was particularly inspired by Jan Groenewegen’s model of innovation according to which the rate of change depends on the granularity of change. Can a new protocol be adopted by individuals, or does it need companies to adopt it en masse for internal use, or does it need to spread through a whole ecosystem, or – the hardest case of all – does it require a change in culture, norms or values?

Security engineers tend to neglect such “soft” aspects of engineering, and we probably shouldn’t. So we sketch a model of the innovation stack for security and draw a few lessons.

Perhaps the most overlooked need in security engineering, particularly in the early stages of a system’s evolution, is recourse. Just as early ATM and point-of-sale system operators often turned away fraud victims claiming “Our systems are secure so it must have been your fault”, so nowadays people who suffer abuse on social media can find that there’s nowhere to turn. A prudent engineer should anticipate disputes, and give some thought in advance to how they should be resolved.

Reconciling Multiple Objectives appeared at Security Protocols 2017. I forgot to put the accepted version online and in the repository after the proceedings were published in late 2017. Sorry about that. Fortunately the REF rule that papers must be made open access within three months doesn’t apply to conference proceedings that are a book series; it may be of value to others to know this!

Bitter Harvest: Systematically Fingerprinting Low- and Medium-interaction Honeypots at Internet Scale

Next week we will present a new paper at USENIX WOOT 2018, in which we show that we can find low- and medium-interaction honeypots on the Internet with a few packets. So if you are running such a honeypot (Cowrie, Glastopf, Conpot etc.), then “we know where you live” and the bad guys might soon as well.

In total, we identify 7,605 honeypot instances across nine different honeypot implementations for the most important network protocols SSH, Telnet, and HTTP.

These honeypots rely on standard libraries to implement large parts of the transport layer, but they were never intended to provide identical behaviour to the systems being impersonated. We show that fixing the identity string pretending to be OpenSSH or Apache and not “any” library or fixing other common identifiers such as error messages is not enough. The problem is that there are literally thousands of distinguishing protocol interactions, part of the contribution of the paper is to show how to pick the “best” one. Even worse, to fingerprint these honeypots, we do not need to send any credentials so it will be hard to tell from the logging that you have been detected.

We also find that many honeypots are deployed and forgotten about because part of the fingerprinting has been to determine how many people are not actively patching their systems! We find that  27% of the SSH honeypots have not been updated within the last 31 months and only 39% incorporate improvements from 7 months ago. It turns out that security professionals are as bad as anyone.

We argue that our method is a  ‘class break’ in that trivial patches cannot address the issue. Thus we need to move on from the current dominant honeypot architecture of python libraries and python programs for low- and medium-interaction honeypots. We also have developed a modified version of the OpenSSH daemon (sshd) which can front-end a Cowrie instance so that the protocol layer distinguishers will no longer work.

The paper is available here.