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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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
204 views

Is there any security risk with adding a **root's** public key to the local user's authorized_keys (so root to login as a user non-interactively?)

Background: I want to try unprivileged lxc containers a try on my small web server (hosting 2-4 users). Since the server is shared among friends, we decided to separate our services from the machine ...
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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
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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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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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1answer
35 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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120 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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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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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
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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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Does RekeyLimit property in sshd_config enforce re-keying / key re-exchange?

I have set the RekeyLimit property in sshd_config and tried to perform a SSH. However, I could not see rekeying happening in the verbose logs, all I see is the log message below at the start of the ...
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1answer
31 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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6answers
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Is using a public-key for logging in to SSH any better than saving a password?

Using a public/private key pair is fairly convenient for logging in to frequented hosts, but if I'm using a key pair with no password, is that any safer (or less safe) than a password? The security ...
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1answer
109 views

System breach or OpenSSH glitch?

The system runs a SSH daemon, and a nginx web server, both ports being open to the internet. We are part of a university so our ports are forwarded from the main router to the intranet. At about ...
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1answer
167 views

Why does the server ssh public key not look like the key in client known hosts?

From my naive understanding of ssh, the server shares its public key ( /etc/shh/ssh_host_rsa_key.pub ) with the client, who then adds it to the list of known hosts ( /user/.ssh/known_hosts ). So, I ...
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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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11answers
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What alternatives are there when SSH is being actively filtered?

Unfortunately our government filters the SSH protocol so now we can't connect to our Linux server. They do the filtering by checking the header of each packet in the network layer (and not by just ...
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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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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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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
208 views

SSH ciphers, MAC and key-exchange (and pen-tests thereof)

At work we've been trying to move our external-facing services away from a policy of inclusivity (where we tried to accept as many people as possible) to a more security-focused setup. The first step ...
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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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Can a user verify the quality/safety of pregenerated SSH moduli parameters?

Many tutorials about how to mitigate the Logjam recommend regenerating Diffie-Hellman moduli. This is a resource intensive operation, especially for high-bit groups. This made me think if it made ...
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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
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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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2answers
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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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3answers
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How to harden SSH on CentOS 6.5

I have a new (first time) CentOS 6.5 server being used for a web server. Our security team has identified the following weakness: The SSH server is configured to allow either MD5 or 96-bit MAC ...
3
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1answer
48 views

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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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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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
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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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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 ...
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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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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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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
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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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How exploitable is the recent UseRoaming SSH problem?

I recently heard about a serious bug in an OpenSSH client (CVE-2016-0777 and CVE-2016-0778) that if I understood correctly could cause remote code execution. How difficult would be for an active ...
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4answers
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Managing multiple SSH private keys for a team

I have a medium-sized team (~10 people, but we expect to grow) that manages a set of EC2 servers on AWS (currently a few dozens, but this is also expected to grow). As EC2 requires you to have an ...
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1answer
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Yubikey / GPG with OpenSSH signed key

I am currently looking into the possibility of using Yubikey (NEO)'s to store the private SSH keys of my users. By searching the internet I've found several places that explain how you can generate a ...
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5answers
732 views

Bastion host that allows jailed users to SSH but protects private key

Basically, I'm trying to let the user use a private key without having read access to it. Use case: Employee needs to SSH to a server in the data center. There is 1 private key for all servers, ...
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1answer
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
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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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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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signing private openssl key for use with openssh

This is related to Converting keys between openssl and openssh . I have private keys generated by openssl that I want to use with SSH for connection authentication. I have no issue using ssh-keygen ...
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3answers
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Secure Configuration of Ciphers/MACs/Kex available in SSH

Following on the heels of the previously posted question here, Taxonomy of Ciphers/MACs/Kex available in SSH?, I need some help to obtain the following design goals: Disable any 96-bit HMAC ...
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1answer
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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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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 ...
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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 ...