Linux-Fu: Applications On The Web

Did you know you can run remote Linux GUI programs in a browser with HTML5 support? It’s even secure because you can use SSH tunneling and that little trick means you don’t even need to open additional ports. If this sounds like gibberish, read on, it’s actually pretty easy to get up and running.

I recently was a guest on a Houston-based podcast, and the hosts asked me if the best thing about writing for Hackaday was getting to work with the other Hackaday staff. I told them that was really good, but what I like best was interacting with people (well, most people) in the comments. That sometimes you’d post an article and someone would bring a topic up in comments that would really knock your socks off. This is how I wound up with this nearly ideal remote access solution, that requires nothing on the remote side but a web browser.

A while back I posted about keeping programs running after log off on a Linux box. The post was mostly about non-GUI programs but you could use NX or VNC to handle it. In the comments, someone mentioned how unhappy they’d been with recent copies of NX and another commenter called [Screen for X11] posted about a tool called xpra.

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A Red Teamer’s Guide To Pivoting

What is hacking and what is network engineering? We’re not sure where exactly to draw the lines, but [Artem]’s writeup of pivoting is distinctly written from the (paid) hacker’s perspective.

Once you’re inside a network, the question is what to do next. “Pivoting” is how you get from where you are currently to where you want to be, or even just find out what’s available. And that means using all of the networking tricks available. These aren’t just useful for breaking into other people’s networks, though. We’ve used half of these tools at one time or another just running things at home. The other half? Getting to know them would make a rainy-day project.

Is there anything that ssh and socat can’t do? Maybe not, but there are other tools (3proxy and Rpivot) that will let you do it easier. You know how clients behind a NAT firewall can reach out, but can’t be reached from outside? ssh -D will forward a port to the inside of the network. Need to get data out? There’s the old standby iodine to route arbitrary data over DNS queries, but [Artem] says dnscat2 works without root permissions. (And this code does the same on an ESP8266.)

Once you’ve set up proxies inside, the tremendously useful proxychains will let you tunnel whatever you’d like across them. Python’s pty shell makes things easier to use, and tsh will get you a small shell on the inside, complete with file-transfer capabilities.

Again, this writeup is geared toward the pen-testing professional, but you might find any one of these tools useful in your own home network. We used to stream MP3s from home to work with some (ab)use of netcat and ssh. We keep our home IoT devices inside our own network, and launching reverse-proxies lets us check up on things from far away without permanently leaving the doors open. One hacker’s encrypted tunnel is another man’s VPN. Once you know the tools, you’ll find plenty of uses for them. What’s your favorite?

Thanks [nootrope] for the indirect tip!

Giving Linux The Remote Boot

A lot of embedded systems are running Linux on platforms like Raspberry Pi. Since Linux is fully functional from a command line and fully network-capable, it is possible to run servers that you’ve never had physical access to.

There are a few problems, though. Sometimes you really need to reboot the box physically. You also need to be at the console to do things like totally install a new operating system. Or do you? Over on GitHub, user [marcan] has a C program and a shell script that allows you to take over a running system without using any software on the root filesystem. It starts an ssh server and you can remotely unmount the main drive, do any maintenance you want and –presumably–reboot into a new operating system.

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Grant Anyone Temporary Permissions To Your Computer With SSH

This is a super cute hack for you Linux users out there. If you have played around with SSH, you know it’s the most amazing thing since sliced bread. For tunneling in, tunneling out, or even just to open up a shell safely, it’s the bees knees. If you work on multiple computers, do you know about ssh-copy-id? We had been using SSH for years before stumbling on that winner.

Anyway, [Felipe Lavratti]’s ssh-allow-friend script is simplicity itself, but the feature it adds is easily worth the cost of admission. All it does is look up your friend’s public key (at the moment only from GitHub) and add it temporarily to your authorized_keys file. When you hit ctrl-C to quit the script, it removes the keys. As long as your friend has the secret key that corresponds to the public key, he or she will be able to log in as your user account.

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SSH Enters The Mosh Pit

With so many systems depending on Linux, the secure shell SSH has become a staple for many developers. If you are connected to your Raspberry Pi via a cable or a wireless router a few feet away, SSH can provide you with an encrypted connection straight to the box. However, if you have a system out in a swamp somewhere with intermittent slow network access, SSH can be a real pain. When your IP address can change (for example, roaming on a cellular network), SSH has problems, too.

To combat these and other problems, you might consider an open source program called Mosh (mobile shell). There’s two parts to Mosh. One part works as a server while the other is the client application. Neither of these require root access. You can see a video about Mosh below.

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When Your Screen Breaks In The Himalayas

If you’ve ever had the screen break on your laptop, you’ll know it can be rather annoying to have to use an external monitor for a while as you either wait for a replacement panel to arrive from the other side of the world, or wait for that new laptop you were just desperate for an excuse to upgrade to.

Spare a thought, then, for [tom bh] whose laptop screen broke while he was in Ladakh, Northern India. Two days bus ride from the nearest city in which he could hope to source a replacement part, he had to make do with the resources in front of him. A laptop with a broken screen, and his Android phone.

He was fortunate in that a few lines at the top of the screen still worked intermittently. So after logging in blind and finding himself in a shell, he could execute commands and then scroll the results up to the point at which they were visible. He first enabled an SSH server, then connected his phone via USB. A bit of work to find the laptop’s IP address, and he could get himself a laptop shell on his phone with an Android SSH client. He goes into detail about how he was able to use the laptop’s keyboard to emulate a Bluetooth device which he connected to the phone. He could then run a VNC server on the laptop and connect to it with a VNC client on the phone, resulting in a phone-sized laptop display using the laptop’s keyboard as input. Not a perfect physical terminal by any means, but enough for him to continue working.

His writeup is an especially interesting read for its side-by-side evaluation of the various different application choices he made, and contains some useful suggestions as to how anyone might prepare themselves for a dead screen related emergency.

We’ve featured a dead-screen laptop connected as a serial terminal with an Arduino in the past, but unlike this one that only gave its owner a prompt.

Via Hacker News.

Lock Up Your Raspberry Pi With Google Authenticator

Raspberry Pi boards (or any of the many similar boards) are handy to leave at odd places to talk to the network and collect data, control things, or do whatever other tasks you need a tiny fanless computer to do. Of course, any time you have a computer on a network, you are inviting hackers (and not our kind of hackers) to break in.

We recently looked at how to tunnel ssh using a reverse proxy via Pagekite so you can connect to a Pi even through firewalls and at dynamic IP addresses. How do you stop a bad guy from trying to log in repeatedly until they have access? This can work on any Linux machine, but for this tutorial I’ll use Raspberry Pi as the example device. In all cases, knowing how to set up adequate ssh security is paramount for anything you drop onto a network.

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