SSH (Secure shell) is a protocol for secure communication between computers to execute remote commands, transfer data and tunnel TCP connections.

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What is the best practice to secure an unattended Raspberry Pi?

I'm working on a project which involves mounting a Raspberry Pi on a self-moving vehicle. I'm looking for the best way to encrypt the Pi (entire file-system, swap, etc.), with the minimum possible ...
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What can possibly happen to a public SSH server?

I'm writing a console emulator in JQuery, which will connect to a server through SSH and dynamically send commands (through AJAX) and receive output. Basically it will be a remote ssh console on a ...
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4answers
3k views

Does FTPS (FTP+S) offer better security than SFTP on the server side?

I had an exchange with some third party sysadmin yesterday regarding the setup of a file transfer interface between our servers. I suggested using SFTP because our application has good support for ...
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5answers
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Advantages to killing sessions after 5 minutes?

I'm dealing with a server that isn't mine to configure. Something somewhere between me and this server kills any connection after 5 minutes if no traffic passes between the two machines. This includes ...
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1answer
33 views

Which ssh exploit works by changing the user name in the middle of the process?

Every few hours, I get a few of those in my server logs: sshd[...]: Disconnecting: Change of username or service not allowed: (httpd,ssh-connection) -> (http,ssh-connection) [preauth] sshd[...]: ...
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117 views

My server was hacked and files have been deleted

Today I got a message when I logged on the server: Hi, please view: http://pastie.org/private/tlixxvclirxmut6djqyacq for further in ...
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1answer
27 views

SSH Tunnels for Securing IoT Sensor-to-Server Connections (Many to One)

All, How bad (or good) an idea would it be to utilize SSH tunnels from my sensor gathering remote computers (imagine an "industrial" Raspberry Pi-like device w/ Linux) to my centralized server (also ...
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Best practices: Use of a single private key as a person, or multiple to identify self across domains?

Similar to the question here, I'd like to apply the same question to a person. For example, I have implanted a chip in my hand that holds an encrypted private key that serves as my personal unique ...
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How does ssh choose the correct key to use? [migrated]

How does ssh-agent understand which key should it use for which remote server? I've came across different questions and posts that touches this topic somehow, but it still remain unclear to me. What ...
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1answer
20 views

SSH session_id in RFC 4253 (key exchange)

in RFC 4253 "SSH Transport Layer Protocol", section 7.2 specifies how session encryption and integrity keys (and IVs) are derived from the shared secret (K) and the exchange hash value (H). It uses, a ...
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Why would I sign my git commits with a GPG key when I already use an SSH key to authenticate myself when I push?

Simply put, I am wondering why would one need to sign one's commits with a GPG key when contributing to GitHub when one's already required to provide an SSH public key?
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30 views

X windows security: VNC and X server vs xpra

I have a CentOS server that currently has no X server on it. It will be used for doing statistical crunching and providing other services (probably via a web interface). The main security for the ...
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Connection refused when trying to SSH. But port 22 is not blocked. Pings work [migrated]

Connection refused when trying to SSH. But port 22 is not blocked. Pings work. I'm running CentOS 7 VMs and open source Docker. I want to SSH to Docker containers from other VMs or other Docker ...
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1answer
107 views

Can my company see that i'm using SSH?

In my company we use our own notebooks. Due to web filters, I decided to create an SSH tunnel to use my home internet connection. My question is: can my company identify that I'm using SSH? I've ...
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1answer
102 views

Someone logged in server through ssh using my RSA key

I just got the warning message from hosting provider that my server make outcoming traffic 1.5G to provide DDOS attack on someone host, and they disabled my VPS temporarily. When I search through ...
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41 views

find owner of private key

On one of the old dev servers I manage there is an RSA public and private key pair ~/.ssh/id_rsa.pub and ~/.ssh/id_rsa in a staging user account (used for automation and testing prior to ...
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1answer
36 views

Encrypt existing SSH key

I've created an RSA keypair for ssh access to a remote server. This all works. When creating the keypair, I didn't enter a password. Now I would like to encrypt the key, secure it with a password. Is ...
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2answers
34 views

Would saving GPG and SSH keys as another user improve security?

Since e.g. SSH keys under Linux are owned by the user who created them, any applications running as the user, e.g. a web browser, should be able to read them from the ~/.ssh folder. Say that there is ...
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Public key for SSH over the internet differs from a key for SSH over the LAN

I have a Raspberry Pi and can access it via SSH (authentication via user password) when my laptop is in the same network. Now I want to access it over the internet. I already set my router to forward ...
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1answer
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Security of only allowing a few vetted commands using $SSH_ORIGINAL_COMMAND

Using a authorized_keys forced command with ssh and a wrapper-script like this: #!/usr/bin/env bash case "$SSH_ORIGINAL_COMMAND" in /var/lib/authorized-scripts/*) $SSH_ORIGINAL_COMMAND ;; ...
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1answer
48 views

Is symmetric encryption with one time pre-shared key secure?

Suppose I have a secure channel between client and server, with proper certificate validation etc (actually, ssh session). I want to establish a secure connection between my own application on a ...
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1answer
56 views

Is it reckless to use an Android app to login to a server with SSH?

There is a very similar question here. Recently I came across an Android app that facilitates SSH and requires no permissions. Specifically, "Telnet / SSH Simple Client" by Advanced Planning Corp.. ...
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Tunneling rdp over ssh as a network newbie

For whatever reason I need to access a virtual machine (Windows server 2008r2) on my home network from outside the network over the internet via remote desktop. I read that there are "concerns" with ...
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1answer
29 views

Is it safe to use an Android Server Monitoring App, to login to a server with SSH?

Lately I have seen some Android Apps, (CPU Monitoring and things like that) that need access to your root account, ask you for username and pass, my questions are: Is it safe to give access to an ...
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1answer
158 views

How long to re-seed /dev/urandom in a virtual machine?

I have read plenty about the distinction between /dev/random and /dev/urandom. I understand that the prevailing advice is to use /dev/urandom. The explanation - that 256 bits of 'proper' randomness ...
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35 views

What purpose is served by repeated connection resets?

My server logs are being filled with Connection Reset by xxx.xxx.xxx.xxx [preauth]: $ cat /var/log/auth.log | grep 'Connection Reset' Mar 13 19:52:30 server sshd[29366]: Connection reset by ...
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1answer
40 views

What are the dangers of exposing weakly protected user accounts bound with a fake shell over ssh?

As anyone running a server can tell from first-hand experience, there are bots trying to constantly brute force their way through with commonly found usernames over SSH. A friend of mine created a ...
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1answer
59 views

How can I enforce that an SSH private key has a passphrase?

My company is serious about security and willing to move to SSH key-pairs. Users can generate their SSH key pairs independently and I worry if they set a pass-phrase. Can I enforce this? Does signing ...
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1answer
60 views

openssh old version vulnerabilities

My Ubuntu 12.04LTS system currently offers OpenSSH_5.9p1 Debian-5ubuntu1.8, OpenSSL 1.0.1 14 Mar 2012. Besides being old, it does not allow me to use e.g. the option # PubkeyAcceptedKeyTypes ssh-rsa* ...
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1answer
156 views

How did hackers compromise my EC2 instance?

My EC2 instance was hacked recently. It doesn't really matter as I'm just starting my website and there was no sensitive information on my server yet, but I do plan for there to be in the future. I am ...
3
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1answer
97 views

Putty settings - Protocols and Algorithms to warn about

I specify "Putty" as otherwise I feel the question would be too broad. What are the algorithm (as of March 2016) that one needs to be warned about (ie, those that no longer are considered safe ...
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SSH and Port Forwarding - what are the possible attacks and how to avoid them? [closed]

What are possible attacks when using SSH and Local or Remote Port Forwarding? What are the threats? I understand that there are many, but what are they? And also, how could they be avoided?
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Minimal working configuration for reasonable security in openssh on Linux [duplicate]

I want to connect from my laptop to home server (both run some Linux; notice I explicitly want my user to be able to become root, in order e.g. to install new software): the server has the following ...
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1answer
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Why does the result of ssh-keyscan -H contain a header line with the un-hashed server ID?

I'm attempting to build a global known_hosts file for my AWS VPC, and was looking at using ssh-keyscan to acquire the fingerprints of new servers as they are created. The -H option seems sensible, as ...
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Can I use process crash information to detect buffer overflow attacks?

Buffer overflow is a very common vulnerability, often targeted with zero-day exploits. Successful attacks often result in arbitrary code execution, while failed attempts tend to crash the target ...
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1answer
49 views

Connecting to a compromised server

There have been a number of threads lately about hacked websites where attackers are gaining control of the servers these sites are being hosted on. As such, these servers should be treated as ...
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1answer
51 views

What are the privacy implications of using Yubico OTP with YubiCloud?

I am considering purchasing Yubikey devices (made by Yubico) to add two-factor authentication when my users ssh to our various servers. I figured I would configure the device to use Yubico OTP with ...
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2answers
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Can someone explain how sshd does privilege separation?

I'm confused about how sshd drops privs for incoming connections. I found this page which was very informative on a high level: http://www.citi.umich.edu/u/provos/ssh/privsep.html But I don't ...
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Snort “Protocol mismatch” from SSH preprocessor

TL;DR -- What does "protocol mismatch" even mean, and how is this a threat? Can I just suppress it? We are busy tuning Snort. The SSH preprocessor section looks like this, which comes directly from ...
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1answer
57 views

ssh key strength

Github currently suggest this type of key: ssh-keygen -t rsa -b 4096 -C "your_email@example.com" Is there a stronger algorithm or byte length mostly usable for most contemporary cloud, PaaS and ...
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How to secure shared user on build server?

We have a CI server which is installed as the builduser and all tasks are executed as that respective user at the OS level. We have many teams sharing the build server which means the build user and ...
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3answers
2k views

how does reverse shell behave?

Someone was helping me with a problem on my vagrant server. He was able to access shell via (I ran it for him, with his ip and port): nc <ip> -e /bin/bash <port> I've never encountered ...
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1answer
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Spoofing LAN IP Address Traffic

To give as much detail as possible, I am doing a Pentest for a client that has quite a few "terminal systems" meaning that they are simply a box with a connection back to the main server. These ...
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4answers
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Running SSH on a different port vs adding the port number to a password

So, a pretty typical piece of advice is to run SSH on a high port number, thus decreasing the chances of it being attacked. The thing I have always wondered about though is that it seems more secure ...
5
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1answer
62 views

Is OpenSSL generating Diffie-Hellman parameters that are safe for use in TLS or SSH servers?

I would like to generate Diffie-Hellman parameters on a Debian GNU/Linux "Jessie" 8 with OpenSSL. Lets assume the system CSPRNG was seeded with some real random data. On such a system, is the result ...
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1answer
205 views

There might be a man in the middle attack against my server

I have a little $7.20/y VPS, and the fingerprint for the ECDSA key has changed three times on me. This time, it happened shortly after I reinstalled the server (same day, in fact.) I always disable ...
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Should different versions of SSH give different VisualHostKeys?

I am SSHing to a server via Cygwin's SSH and via Ubuntu 14.04's SSH. Cygwin version: OpenSSH_7.1p2, OpenSSL 1.0.2e 3 Dec 2015 Ubuntu version: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4, OpenSSL 1.0.1f 6 Jan ...
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1answer
562 views

Why OpenSSH deprecated DSA keys

There was a question RSA vs. DSA for SSH authentication keys asking which key is better. Basically all answers were more in a favour of RSA over DSA but didn't really tell that DSA would be somehow ...
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6answers
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Why is leaving a passworded SSH over the internet so bad?

I've heard multiple multiple times to never leave SSH with a password open over the internet. Why is this so bad? I understand the password can be bruteforced, but what if it is a very strong ...
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5answers
2k views

Should I use a second/dedicated IP address for SSH?

When running a public web server (e.g., with Apache), I've heard it's recommended to bind SSH to a second IP address, different from the one Apache is listening to. But for me it seems like this is ...