This Week In Security: Triangulation, ProxyCommand, And Barracuda

December 29, 2023 by Jonathan Bennett 6 Comments

It’s not every day we get to take a good look inside a high-level exploit chain developed by an unnamed APT from the western world. But thanks to some particularly dedicated researchers at Kaspersky, which just happens to be headquartered in Moscow, that’s exactly what we have today. The name Operation Triangulation was picked, based off part of the device fingerprinting code that rendered a yellow triangle on an HTML canvas.

The entire talk is available, given this week at the 37th Chaos Communication Congress, 37c3. The exploit starts with an iMessage attachment, delivered silently, that exploits an undocumented TrueType font instruction. Looking at the source code implies that it was a copy-paste error where a programmer didn’t quite get the logic right for a pointer calculation. That vulnerability gives a memory write primitive that pivots into code execution. What’s particularly interesting is that Apple silently fixed this bug January 2023, and didn’t make any public statements. Presumably there were an uptick of crash logs that pointed to this problem, but didn’t conclusively show attempted exploitation.

The exploits then moves to using NSExpression as a next stage. NSExpression is an ugly way to write code, but it does allow the exploit chain to get to the next stage, running JavaScript as an application, without Just In Time compilation. The JS payload is quite a beast, weighing in at 11,000 lines of obfuscated code. It manages to call native APIs directly from JS, which then sets up a kernel exploit. This is multiple integer overflow flaws that result in essentially arbitrary system memory reads and writes. Continue reading “This Week In Security: Triangulation, ProxyCommand, And Barracuda” →

This Week In Security: SSH, FTP, And Reptar

November 17, 2023 by Jonathan Bennett 3 Comments

It’s time to strap on our propeller beanies, because we’re going to talk crypto. The short version is that some SSH handshakes can expose enough information for a third party to obtain the host’s private signing key. That key is the one that confirms you are connecting to the SSH server you think you are, and if the key validation fails, you get a big warning:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!

The math that makes this warning work is public-private key cryptography. The problem we’re talking about today only shows up in RSA authentication. Specifically those that use the Chinese Remainder Theorem (CRT) to quickly calculate the modulos needed to generate the cryptographic signature. If something goes wrong during that calculation, you end up with a signature that is mathematically related to the secret key in a different way than intended. The important point is that knowing this extra value *significantly* weakens the security of the secret key.

This attack has been known for quite some time, but the research has been aimed at causing the calculation fault through power vaults or even memory attacks like Rowhammer. There has also been progress on using a lattice attack against captured handshakes, to make the attack practical with less known information. The real novel element of this week’s approach (pdf) is that it has been tested against SSH.

The paper’s authors performed weekly scans of the entire IPv4 public network space, capturing the handshake from any listening SSH server, and also had 5 years of historic data to draw from. And the results are mixed. There is a Cisco SSH server string that is extremely common in the dataset, and only once did one of these machines send a miscalculated handshake. Possibly a random ram bit flip to blame. And on the other hand, the string “SSH-2.0-Zyxel SSH server” had so many bad signatures, it suggests a device that *always* sends a miscalculated signature. Continue reading “This Week In Security: SSH, FTP, And Reptar” →

SSH Can Handle Spaces In Command-line Arguments Strangely

July 15, 2023 by Donald Papp 48 Comments

One of the things ssh can do is execute a command on a remote server. Most of us expect it to work transparently when doing so, simply passing the command and its arguments on without any surprises in the process. But after 23 years of using OpenSSH on a nearly daily basis, [Martin Kjellstrand] got surprised.

It turns out that the usual rules around how things are parsed can have some troublesome edge cases when spaces are involved. [Martin] kicks off an example in the following way:

One would reasonably expect the commands figlet foobar bar\ baz and ssh localhost figlet foobar bar\ baz to be functionally equivalent, right? The former ultimately runs the command “figlet” with arguments “foobar” and “bar baz” on the local machine. The second does the same, except with ssh being involved in the middle. As mentioned, one would expect both commands to be functionally identical, but that’s not what happens. What happens is that ssh turns bar\ baz into two distinctly separate command-line arguments in the process of sending it for remote execution: “bar” and “baz”. The result is mystification as the command fails to run the way the user expects, if it runs at all.

What exactly is going on, here? [Martin] goes into considerable detail tracking down this odd behavior and how it happens, but he’s unable to ultimately explain why ssh does things this way. He suspects that it is the result of some design decision taken long ago. Or perhaps a bug that has, over time, been promoted to entrenched quirk.

Do you have any insights or knowledge about this behavior? If so, [Martin] wants to hear about it and so do we, so don’t keep it to yourself! Let us know in the comments, below.

SSH Is Magic, But Tunnels Are Even Better

April 24, 2022 by Jonathan Bennett 17 Comments

Once upon a time, I was doing on-site support for a hardware install at a hotel a few years ago. The remote tech’s remote desktop software didn’t want to play with my Linux laptop, so he couldn’t get into the switch he needed to configure, to make the install work. I asked if it had an SSH port he could use, were he were in the room with me. Of course it did, but that didn’t do him much good. I ran a reverse SSH tunnel out to my public server, and pointed it at the switch on the local side. I convinced him to SSH to my server on the given port, and he was magically connected to his switch. He was literally in awe of that trick, and demanded to know how it could be done. SSH is magical, but tunneling traffic over SSH is straight-up wizardry. [Shawn Powers] agrees, and decided to help the rest of us understand the process.
Continue reading “SSH Is Magic, But Tunnels Are Even Better” →

This Horrifying Robot Is Here To Teach You A Lesson

July 1, 2021 by Tom Nardi 8 Comments

No, despite what it might look like, this isn’t some early Halloween project. The creepy creation before you is actually a tongue-in-cheek “robot” created by the prolific [Nick Bild], a topical statement about companies asking their remote workers to come back into the office now that COVID-19 restrictions are being lifted. Why commute every day when this ultra realistic avatar can sit in for you?

OK, so maybe it’s not the most impressive humanoid creation to ever grace the pages of Hackaday. But if you’re looking to spin up a simple telepresence system, you could do worse than browsing through the Python source code [Nick] has provided. Using a Raspberry Pi 4, a webcam, and a microphone, his client-server architecture combines everything the bot sees and hears into a simple page that can be remotely accessed with a web browser.

Naturally this work from home (WFH) bot wouldn’t be much good if it was just a one-way street, so [Nick] has also added a loudspeaker that replays whatever he says on the client side. To prevent a feedback loop, his software includes a function that toggles which direction the audio stream goes in by passing the appropriate commands to the bot over SSH; a neat trick to keep in mind for your own, less nightmarish, creations.

If you’re looking for something a bit more capable and have some cardboard laying around, this DIY telepresence mount for your phone might be a good place to start.

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Linux Fu: VPN For Free With SSH

November 23, 2020 by Al Williams 44 Comments

If you see a lot of banner ads on certain websites, you know that without a Virtual Private Network (VPN), hackers will quickly ravage your computer and burn down your house. Well, that seems to be what they imply. In reality, though, there are two main reasons you might want a VPN connection. You can pay for a service, of course, but if you have ssh access to a computer somewhere on the public Internet, you can set up your own VPN service for no additional cost.

The basic idea is that you connect to a remote computer on another network and it makes it look like all your network traffic is local to that network. The first case for this is to sidestep or enhance security. For example, you might want to print to a network printer without exposing that printer to the public Internet. While you are at the coffee shop you can VPN to your network and print just like you were a meter away from the printer at your desk. Your traffic on the shop’s WiFi will also be encrypted.

The second reason is to hide your location from snooping. For example, if you like watching the BBC videos but you live in Ecuador, you might want to VPN to a network in the UK so the videos are not blocked. If your local authorities monitor and censor your Internet, you might also want your traffic coming from somewhere else.

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Displaying Incoming Server Attacks By Giving Server Logs A Scoreboard

September 23, 2020 by Bryan Cockfield 9 Comments

In the server world, it’s a foregone conclusion that ports shouldn’t be exposed to the greater Internet if they don’t need to be. There are malicious bots everywhere that will try and randomly access anything connected to a network, and it’s best just to shut them off completely. If you have to have a port open, like 22 for SSH, it’ll need to be secured properly and monitored so that the administrator can keep track of it. Usually this is done in a system log and put to the side, but [Nick] wanted a more up-front reminder of just how many attempts were being made to log into his systems.

This build actively monitors attempts to log into his server on port 22 and notifies him via a numerical display and series of LEDs. It’s based on a Raspberry Pi Zero W housed in a 3D-printed case, and works by interfacing with a program called fail2ban running on the server. fail2ban‘s primary job is to block IP addresses that fail a certain number of login attempts on a server, but being FOSS it can be modified for situations like this. With some Python code running on the Pi, it is able to gather data fed to it from fail2ban and display it.

[Nick] was able to see immediate results too. Within 24 hours he saw 1633 login attempts on a server with normal login enabled, which was promptly shown on the display. A video of the counter in action is linked below. You don’t always need a secondary display if you need real-time information on your server, though. This Pi server has its own display built right in to its case.

Continue reading “Displaying Incoming Server Attacks By Giving Server Logs A Scoreboard” →