Questions tagged [ssh]
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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YubiKey Bio for SSH login: Do I have to reauthenticate?
I'd like to use YubiKey Bio for SSH-logins. I'm wondering how often I have to show my fingerprint for authentication when I start new sessions. What's the interval? If I start a new session every 5 ...
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RSA vs Shor's Algorithm/Fast Factoring — Server Credentials & MITM
I've watched a lot of videos on Shor's Algorithm and Quantum Computers. Most of these videos say these two things undermine RSA via fast-factoring, but they never really explain how fast-factoring is ...
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How do programs store plain-text secrets securely? [duplicate]
The best example, would be the ~/.ssh folder, or the linux keychain.
Why is the ~/.ssh folder considered safe? When researching this, people said that the permissions of the folder would give enough ...
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Consequences of .ssh/authorized_keys being world-readable
OpenSSH sshd enforces mode 0600 for authorized_keys when StrictMode is enabled. How is mode 0644 more vulnerable?
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Outdoor backup: gocryptfs --init --reverse: alway same .diriv in 1st level directory
Intro
Trying to send encrypted backup of in productions filesystems, I was interested by the ability of using gocryptfs in reverse mode!
The idea is to
use gocryptfs --reverse from any existing (...
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Upgrade MSF ssh to meterpreter on a host behind a forwarded host
I'm training on a test network. I managed to snatch some ssh credentials and spawn a shell with msfconsole. Turns out a connection via ssh to 192.168.0.3:2222 forwards me to 192.168.0.4:22. So I have ...
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PCI DSS 4.0 - Are SSH tunnels and gateways doomed?
I won't lie, I am not a security expert and I am likely one of them guys in them companies whom working life proficiency is to slowly become little annoying. I work for a company complying with PCI ...
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How to update Ubuntu SSH version to latest version [closed]
I'm trying to update the Ubuntu OpenSSH version to 9.3p2, because of the CVE-2023-38408 vulnerability, but I can't.
The recomendation is update to last version: https://ubuntu.com/security/CVE-2023-...
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Making sure that SSH key is NOT used anywhere but specific hosts
I have an SSH key for work that I do NOT want to be offered by the forwarding agent anywhere but the work hosts.
So I thought following ~/.ssh/config could do the trick:
Host *
ForwardAgent yes
...
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What's stopping attackers from brute forcing SSH passwords over new sessions?
I know that when you attempt to log in to a device via SSH, upon inputting an incorrect password, you must wait several seconds before you get another attempt. This is obviously a deterrent against ...
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SSH Login Security - Proxy User with key and su to root
Introduction:
I know this question has been asked many times before in many different forms, but I wanted to come at this in a slightly different way.
I am considering many different ways to secure ...
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SSH ecdsa-sha2 key changed?
I use a yubikey with device-generated ssh keys to login on my servers.
A few months ago I've created a ssh keypair on our cloud provider (OVH) with this value (truncated):
ecdsa-sha2-nistp256 AAAA......
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Advantages of custom ports against cyberattacks [duplicate]
What would be the advantage of binding a common service to a custom port against cybersecurity attacks?
For example I want to make it harder for a hacker to evaluate the attack surface on my server so ...
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SSH - What is the relationship between fingerprint and known_hosts file?
I am trying to understand the relationship between fingerprint of SSH server's public key and known_hosts file.
There are two SSH servers with same public key. I, the client has the private key.
I ...
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Security risk by setting authorized_key for root user and limiting to one command?
Sometimes a process crashes and IT department has to log into the server and do a sudo systemctl restart apache2.
The idea was now to create a wepage an another server (of course) where users can ...
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Why is known_hosts automatically updated but authorized_keys is not?
Referring to this post. We learned about ssh today, and I know that you have to add your public key to the "authorized_keys" manually on the server, but the very first time you log into the ...
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Interaction between sftp subsystem and forced command
I'm responding to a penetration test finding on one of my application servers. The finding is that the private key embedded in my client script is capable of being used to open an SFTP session to the ...
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How outgoing tunnels are not stopped by AV or firewalls?
How can an attacker with initial access to a server behind a firewall, which only has SSH, HTTPS, and HTTP ports open, maintain remote access to the server even after the SSH port is closed by the ...
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Security of SSH with Service like ngrok
I need some help understanding the security implications of using a service like ngrok to setup an ssh connection.
I've got two computers without public IP addresses (both using mobile internet ...
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What standards are there for sharing public SSH fingerprints?
When connecting to a host through SSH for the first time I get met with the message: Authenticity of host ***** can't be established. ECDSA key fingerprint is SHA256 *******. Are you sure you want to ...
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Understanding ssh-rsa not in PubkeyAcceptedAlgorithms
I am having problem in connecting to an Amazon EC2 Linux instance from an old Mac OS machine running El Capitan. Unfortunately without any possibility to upgrade the OS.
Because all the other modern ...
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What are the risks of running SSH over Tor?
Goal
The intention is to set up an SSH entrance which is more secure (or at least more obfuscated) than a default setup with Port Forwarding or VPN.
Previous research and context
TL;DR, see question ...
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Suitable method of encryption for user-hosted chat platforms
I am considering how to make my chat application a bit more secure. It has a similar structure to IRC, multiple users can join each server, and servers can be hosted by anyone. I have been using TLS ...
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Can someone with access to only my Yubikey gain access to my server that has SSH access via an ED25519-sk keypair?
My understanding is that an ED25519-sk SSH key generated by OpenSSH generates a private key stub that lives on your host machine. This stub is just a reference to the actual private key that lives on ...
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Leaving SSH access to deployed on prem server -- why is this bad?
I've recently had a conversation with a colleague (in a new job for me) around access to client's servers which are deployed in their premises.
They have said that allowing ssh access to those servers ...
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Security Implications of Allowing TCP Forwarding to Use vscode-server
While setting up a new VPS instance running Ubuntu, I found that I needed to set AllowTcpForwarding yes in /etc/ssh/sshd_config to achieve a remote VS Code connection. I am and will be the sole user ...
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Why hydra showing this error [ERROR] could not connect to ssh://192.168.0.1:22?
I am using hydra to bruteforce my router admin page. By scanning with nmap it is showing port 22 ssh is open and when i use medusa it is bruteforcing properly but with hydra i am using this command :
...
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How to decrypt SSHv2 using AES-256 session keys from memory dump?
How to decrypt the plaintext contents of an SSH session from a PCAP file and SSHv2 AES session keys from a memory dump.
I have the full PCAP for the SSH sessions, including the initial handshake and ...
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Hydra brute force ssh usernames with given RSA key
On a machine supporting ssh, an RSA key is given but no username.
My idea was brute-forcing the SSH username with Hydra but I didn't find any option to give the RSA key to Hydra.
Is it possible to ...
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Why is cert for localhost not trusted when using ssh tunnel?
I've created a developer cert with my companies CA for my development box.
The CN is the FQDN of my development box mybox.example.com, but I've also added subjectAlternative names that include ...
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Risks and recommendations of using passwordless sudo
Given that I'm the only human who should have access to a Linux server, what are the major security risks associated with updating sudo to not require a password for my local user?
Are there other ...
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Is it possible for a hostname lookup to be temporarily lying (wrong ISP)?
In 2017, I was running a local website on my own dedicated server in a professional data center. FreeBSD. Installed by me remotely. Maintained carefully by me. No other human users than myself. I was ...
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SSH XMSS keypair generation and best practices
In a recent ssh -vv output, I saw OpenSSH mentioning a private key file id_xmss.
XMSS is defined in RFC 8391, "XMSS: eXtended Merkle Signature Scheme", May 2018.
OpenSSH has experimental ...
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Best way to connect to user SSH servers
I have a project that calls users' SSH servers to do some tasks.
For now, I am storing users' passwords at my service as hashed (Username, hashed password and salt), but the SSH password (username, ...
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Securely SSH a server from an intermediary remote machine (possibly with Yubikey)
I am doing remote devevelop on a remote dev machine. From the remote machine, I need to SSH to other servers and services like the Github. Everything is on the Internet. My desktop is much more secure ...
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Securely access server via FTP through SSH tunnel
Is it right to assume, that when i build up a tunnel with ssh -D from outside my LAN and then access my only locally exposed server via FTP, it can be called 'safe'? Tunnel is established on the same ...
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SSH server disconnecting when valid auth request is provided and responding with seemingly invalid SSH_MSG_USERAUTH_PK_OK
I use the net-ssh ruby library to connect to various servers. Around 2 months ago, a large subset of the servers we connect to stopped working, these servers belong to several major banks. We're ...
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Reading SSH private key physically stored on yubikey to remote into external PC
I was wondering if it's possible to only store and read a ssh private key on a yubikey and not read the private key the yubikey generated from a client computer?
Currently the only way it seems to ...
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What can i do with the ssh host key i got from this nmap scan. (Hack the box) [duplicate]
I am on hack the box and I ran nmap -A IP_address and this is the output I received. I am wondering if I can do something with the ssh hostkey.
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SSH over HTTPS or Directly open Non Standard port
We have a situation where we have an architecture that calls for a Web based UI for querying some data and the data input is through rsync over SSH. I think it would be easier to manage and more ...
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SSH authentication with GPG failing with a new Yubikey with the same gpg keys as the old one
I have a MacBook M1 on which I have been using a Yubikey 5 to authenticate SSH logins to various systems. I recently got a Yubikey 5C so I wouldn't have to use adapters. I moved my keys over to it ...
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What would be the security rationale for a hotel blocking only SSH traffic? [closed]
I recently stayed at a hotel where outbound SSH traffic (and seemingly only SSH traffic) was blocked on the guest WiFi network, and I'm trying to figure out what security-based rationale they might ...
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Can an SSH server in password mode be impersonated if I ignore the fingerprint warning?
Assume that I never check the server fingerprint when logging in to an SSH server. This means that certain configurations of SSH can be impersonated. For example, I can log into a server that only has ...
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FTPS with IP restriction OR SFT over SSH without IP restriction - which one is more secure?
Im able to connect to my managed Linux Ubuntu Server only through
FTP using explicit SSL (Auth TLS) with IP restriction
and
SFT over SSH without IP restriction
Question: which method is more secure to ...
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Is brute force for SSH similar to cracking WPA2 handshake?
I heard recently that WPA2 passwords can be brute forced if somebody captures handshake (which is not very difficult). Can somebody tell if a similar method exists for cracking SSH traffic? I mean ...
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Unauthorized firewall rules on SSH bastion servers
Yesterday I found that a few firewall rules (iptables on Ubuntu 20.04 OS) have been added to an SSH bastion server that allow SSH access on a custom SSH port number. All IPs are from Vietnam.
AFAIK ...
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Going about sharing 2FA key between multiple login methods on a Synology NAS + browser & SSH authentication
I've recently acquired a Synology server (DS720+) and have it accessible outside my LAN via a VPN. I have 2FA on for logins to the server via the web portal, but I have found many use cases for ...
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Does the ssh client compute the public key from the private key?
If I use ssh like this ssh -i id_rsa it means im passing the private key to ssh. Does ssh now then compute the public key from it and then send it to the server? Then the server would look if the ...
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Why should I re-generate a server's SSH host keys?
This server hardening guide suggests re-generating the RSA and ED25519 host keys. What is the advantage of re-generating the default key?
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Why should I disable insecure SSH hostkeys if I never plan on using them?
A number of articles suggest removing insecure (broken) SSH key types in order to have a more secure server. In practice, if I only connect to the server with secure key types, why should I bother ...
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