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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Getting Operating System Username using MySQL SQLi

Suppose I have a website which has SQL injection vulnerability and I got the database schema etc. Is there any means by which I can get the operating system username or the SSH username? Asking from ...
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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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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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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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54 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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58 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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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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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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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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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
110 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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116 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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49 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 production)...
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46 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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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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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 ...
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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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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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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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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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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 man-...
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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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432 views

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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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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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 xxx.xxx....
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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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579 views

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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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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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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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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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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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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How to (further) ensure SSH security?

I set up my Linux Ubuntu machine as an SSH server through no-ip.com and it works great. Recently I discovered the command, sudo lastb -ad -F -w which outputs a log of the most recent failed SSH ...
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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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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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SSH key-type, rsa, dsa, ecdsa, are there easy answers for which to choose when?

As someone who knows little about cryptography, I wonder about the choice I make when creating ssh-keys. ssh-keygen -t type, where type is either of dsa,rsa and ecdsa. Googling can give some ...
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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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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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Using SSH Private keys in Production environment

I have a need to scp a bunch of files from a production box to my development environment. I am a developer and have limited read access to the production machines. Instead of entering password for ...