Imagine for a moment the following scenario: you're the manager for a busy bank branch in a major city. You come back from lunch and are told by one of your employees that someone from corporate IT dropped by to check on a reported problem with a branch PC. You don't remember putting in a trouble ticket with IT, but apparently the guy left after looking under a desk and re-plugging a network cable or something. It took less than five minutes. You think nothing of it and go back to approving loans.

Three days later, you get a call from the head of corporate security, wanting to know why someone at your branch has been performing wire transfers from the accounts of customers who've never used your branch to accounts at offshore banks. A few hours later, you're unplugging the bank's network equipment while he's shouting at you over the phone about gigabytes of corporate data being pulled down from something in your bank. And when the security team and police arrive to investigate, they find a little nondescript box plugged into a network port, connected to a broadband cellular modem.

Something like this happened to banks in London last year. A man posing as an IT contractor wired networked keyboard-video-mouse (KVM) switches connected to cellular routers into PCs at two bank branches. The ring involved with the thefts was only caught because they decided to go for a third score, and their "technician" was caught in the act. The digital heists were a variation on the hacker "drop box" strategy: boldly walking into a place of business and planting a device, often hidden in plain sight, to use as a Trojan horse to gain remote access to the business' network.

Drop boxes have another, more law-abiding use in the security business—they allow penetration testers to check the security of organizations' networks. If you don't know what your network's vulnerabilities are, you can't very well defend it. It's why penetration testing has grown from a small but lucrative consulting field to an integral part of some companies' internal security practices. Penetration testing appliances like those made by Pwnie Express (AKA Rapid Focus Security LLC) have made it a lot simpler for all sizes of organizations to do that sort of testing.

Ars has some experience with Pwnie's devices. We used the PwnPlug R2 in our joint project with NPR last summer to act as our NSA-like passive monitoring tool, and then we purchased an R2 for our ongoing security and privacy testing. So when the Pwn Plug R3, the third generation of Pwnie's flagship pen-testing device, arrived on the scene late last year, we decided to give it a thorough workout.

The R3 is a significant step up from its predecessors in a number of ways. There's a lot more under the hood of this device, both in terms of what's been packed within its square shell and the computing power that drives it. While the changes made to Pwnie's software platform are subtle and still evolving, the new hardware brings a lot more power and flexibility to the job. It also comes with a slightly more robust price tag than previous versions: $995.

That seems like a lot for a little black-and-grey box, but a lot of malice has been packed into this small package. And on that note, we apologize again to any neighbors who may have suffered occasionally buggy Wi-Fi as a result of exploring this malice on our own network.

Going corporate

The original Pwn Plug was the first commercialized penetration testing drop box. It looks superficially like a power brick, intended to fool the casual observer. The Pwn Plug R2 upped the ante with a bit more processing and networking power, and it looked like a Wi-Fi access point. At one point, there was even a variant called the Power Pwn disguised as a (working) power strip. (That product is no longer in Pwnie Express' catalog.)

Both previous Plugs relied on low-cost ARM-based hardware packed into small form factors, using SD cards as mass storage. But there were certain limitations to these devices that came with their form factors. For instance, while the original Pwn Plug is still for sale as an "academic edition," Pwnie ran into problems with the R2's manufacturing. Ars' first purchased R2 died, shortly after it was installed, from a heat-related problem, and Pwnie executives acknowledged other customers had similar problems. Pwnie also wanted to beef up the Pwn Plug's hardware to meet other customer demands. Rather than just using the devices for short-term penetration tests, customers were pressing them into service for pervasive surveillance of networks in order to conduct constant security auditing.

At last August's DEF CON, we got a brief hands-on with Pwnie's up-market answer to such requests. The Pwn Pro was the first iteration on the new hardware—an industrial-cased fanless device based on Intel's Next Unit of Computing (NUC) architecture. The Pwn Plug R3 is the more economical, portable version of the same platform, intended like its predecessors as a shippable, portable, pluggable drop box. But it can also plug into some of the capabilities of the Pwn Pro, making it a potential branch-office solution for continuous monitoring of local network security from afar without the need for local support.

The Intel NUC kit the Pwn Plut R3 is based on is not as sneaky as its predecessors—it doesn't disguise itself as a power brick or a Wi-Fi access point. However, the R3 itself isn't about being sneaky. It's about being corporate and legit, while being easily shipped to a location where anyone with basic IT skills can plug it in.

Pumping up the pwnage

TheNUC kit hardware used for thePwn PlugR3 is a 1.1 GHz dual core Celeron processor.Pwnie configures it with two gigabytes ofDDR3 RAM and a 32-gigabyte mSATA SSD drive for fast memory and disk I/O. It comes with just what you want for a packet-processing machine: Wi-Fi, an internal high-gain antenna, and Bluetooth. There's also a gigabit Ethernet port and three USB ports, plus a USB Ethernet adapter to provide a second hard-wired network interface. And all of it is tucked into a nearly square 4.6″×4.4″×1.5″ case.

All that someone needs to do to get the R3 up and running is plug in its external power brick and plug in an Ethernet cable. For cases where there's a need to bypass the target network for remote access, Pwnie provides a USB cellular broadband adapter. Penetration testers can then pre-configure the Pwn Plug to "phone home."

All of this still comes in a form factor, minus the external power brick, that is smaller than most consumer Wi-Fi routers. It could easily be mistaken for an external hard drive or router by anyone giving it a passing glance. And another upside of the small SSD and the NUC's fanless design is that the Pwn Plug R3 is completely silent. The only external indication that it's up to anything is the glowing recessed power button on the top.

Since this is a NUC, there are two HDMI ports on the Pwn Plug R3. That means, unlike its predecessors, you can actually plug a local monitor and keyboard into the Pwn Plug R3 and perform set-up and administrative tasks from a local console. We found that to be a big improvement after our technical contortions to troubleshoot the R2 units used over a USB serial connection.

The core of the Pwn Plug, as always, is its software: Pwnix, a special distribution of Offensive Security's Kali Linux operating system with some proprietary software tools for security testing, remote management, and access. The Pwn Plug can be largely configured and managed through a Web interface, though much of the real work of security auditing still happens with command-line tools.

The Web interface for the Pwn Plug is called Outpost, and it's not the most elaborate Web console ever. Its primary purpose is basic configuration of the Pwn Plug's networking and services, and it also offers a basic console for two of those services: