Day: April 7, 2023

String Operations The Hard(ware) Way

April 7, 2023 by 7 Comments

One of the interesting features of the 8086 back in 1978 was the provision for “string” instructions. These took the form of prefixes that would repeat the next instruction a certain number of times. The next instruction was meant to be one of a few string instructions that operated on memory regions and updated pointers to the memory region with each repeated operation. [Ken Shirriff] examines the 8086 die up close and personal to explain how the 8086 microcode pulled this off and it is a great read, as usual.

In general, the string instructions wanted memory pointers in the SI and DI registers and a count in CX. The flags also have a direction bit that determines if the SI and DI registers will increase or decrease on each execution. The repeat prefix could also have conditions on it. In other words, a REP prefix will execute the following string instruction until CX is zero. The REPZ and REPNZ prefixes would do the same but also stop early if the zero flag was set (REPZ) or not set (REPNZ) after each operation. The instructions can work on 8-bit data or 16-bit data and oddly, as [Ken] points out — the microcode is the same either way.

[Ken] does a great job of explaining it all, so we won’t try to repeat it here. But it is more complicated than you’d initially expect. Partially this is because the instruction can be interrupted after any operation. Also, changing the SI and DI registers not only have to account for increment or decrement, but also needs to understand the byte or word size in play. Worse still, an unaligned word had to be broken up into two different accesses. A lot of logic to put in a relatively small amount of silicon.

Even if you never design a microcoded CPU, the discussion is fascinating, and the microphotography is fun to look at, too. We always enjoy [Ken’s] posts on little CPUs and big computers.

This Week In Security: Cookie Monster, CyberGhost, NEXX, And Dead Angles

April 7, 2023 by 5 Comments

“Operation Cookie Monster” ranks as one of the best code names in recent memory. And it’s apropo, given what exactly went down. Genesis Market was one of those marketplaces where criminals could buy and sell stolen credentials. This one was a bit extra special.

Websites and services are getting better about detecting logins from unexpected computers. Your Google account suddenly logs in from a new computer, and a two-factor authentication challenge launches. Why? Your browser is missing a cookie indicating you’ve logged in before. But there’s more. Providers have started rolling out smart analytics that check for IP address changes and browser fingerprints. Your mix of time zone, user string, installed fonts, and selected language make a pretty unique identifier. So sites like Genesis offer Impersonation-as-a-Service (IMPaaS), which is session hijacking for the modern age.

A victim computer gets owned, and credentials are collected. But so are cookies and a browser fingerprint. Then a criminal buyer logs in, and runs a virtual browser with all that collected data. Run through a proxy to get a IP that is geolocated close enough to the victim, and Mr. Bad Guy has a cloned machine with all accounts intact.

And now back to Operation Cookie Monster, a multi-organization takedown of Genesis. It’s apparently a partial takedown, as the latest word is that the site is still online on the Tor network. But the conventional domains are down, and something like eight million credentials have been captured and added to the Have I Been Pwned database.

Another researcher team, Sector 7, has been working the case with Dutch authorities, and has some interesting details. The vector they cover was a fake activation crack for an antivirus product. Ironic. There are several extensions that get installed on the victim computer, and one of the most pernicious is disguised as Google Drive. This extension looks for a Command and Control server, using Bitcoin as DNS. A hardcoded Bitcoin address is polled for its latest transaction, and the receiving address is actually an encoded domain name, you-rabbit[.]com as of the latest check.

This extension will look for and rewrite emails that might be warning the victim about compromise. Get an email warning about a cryptocurrency withdrawal? It modifies it in the browser to be a sign-in warning. It also allows Genesis customers to proxy connections through the victim’s browser, bypassing IP address security measures. Continue reading “This Week In Security: Cookie Monster, CyberGhost, NEXX, And Dead Angles” →

Arbitrary Code Execution Over Radio

April 7, 2023 by 71 Comments

Computers connected to networks are constantly threatened by attackers who seek to exploit vulnerabilities wherever they can find them. This risk is particularly high for machines connected to the Internet, but any network connection can be susceptible to attacks. As highlighted by security researcher and consultant [Rick Osgood], even computers connected to nothing more than a radio can be vulnerable to attacks if they’re using certain digital modes of communication.

The vulnerability that [Rick] found involves exploiting a flaw in a piece of software called WinAPRS. APRS is a method commonly used in the amateur radio community for sending data over radio, and WinAPRS allows for this functionality on a PC. He specifically sought out this program for vulnerabilities since it is closed-source and hasn’t been updated since 2013. After some analysis, he found a memory bug which was used to manipulate the Extended Instruction Pointer (EIP) register which stores the memory address of the next instruction to be executed by the CPU. This essentially allows for arbitrary code execution on a remote machine via radio.

The exploit was found while using Windows XP because it lacks some of the more modern memory protection features of modern operating systems, but the exploit does still work with Windows 10, just not as reliably and with a bit of extra effort required. It’s a good reminder to use open-source software when possible so issues like these can get resolved, and to regularly install security updates when possible. If you’re looking to delve into the world of APRS in more modern times, take a look at this project which adds APRS to budget transceivers. Just make sure you get your license first.

Building The OhSillyScope

April 7, 2023 by 6 Comments

If you have a Raspberry Pi connected to an LED matrix, you might think about creating a simple oscilloscope. Of course, the Pi isn’t really well-suited for that and neither is an LED matrix, so [Thomas McDonald] decided to create the OhSillyScope, instead.

The device isn’t very practical, but it does add some flash to live music performances or it makes a cool music visualizer. The matrix is only 64×64 so you can’t really expect it to match a proper scope. Besides that, it pulls its data from the Pi’s ALSA sound system.

You can find a video of the device on [Thomas’] Reddit post and a few additional videos on his Instagram account. Looks like a fun project and it also serves as a nice example if you need to read data from the sound card or drive that particular LED matrix.

We might have opted for PortAudio if we had written the same code, but only because it is more portable, which probably doesn’t matter here. Of course, you could also use GNURadio and some Python to drive the display. As usual, plenty of ways to solve any given problem.