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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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OpenSSH 9.6p1: What is the best key type for the ssh-keygen command through the -t option? [duplicate]

The ssh-keygen command to generate the pair of keys files can use the -t option. According to Ubuntu Noble's man ssh-keygen for the mentioned option, it indicates: -t dsa | ecdsa | ecdsa-sk | ed25519 |...
Manuel Jordan's user avatar
4 votes
2 answers
887 views

How to tell if RegreSSHion was exploited (CVE-2024-6387)

I have a VM with a Cloud Provider that I am able to SSH into. I've recently read about RegreSSHion (the reappearance of CVE-2006-5051, as CVE-2024-6387), and I'm wanting to make sure that I wasn't ...
user3517452's user avatar
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15 views

SSH command variants [migrated]

Difference between ssh [email protected] ssh za\\[email protected] ? Both login methods are giving me SSH access but some files/folders are accessible via the latter while not via ...
Aryan's user avatar
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1 answer
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Pentesters: Is it common for bruteforce/ dictionary attacks, e.g. for SSH username enumeration, to be successful in the real-world pentests? [closed]

I am learning and practicing on vulnerable-by-design machines (vulnhub, metasploitable etc.). I found that this machine is running OpenSSH 7.5, and I tried a few exploits of Username enumeration from ...
Shy's user avatar
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1 vote
1 answer
317 views

Now that `sshcontrol` has been deprecated, how to use gpg key for ssh authentication with an agent?

The GnuPG Manual states that: This [sshcontrol] file is deprecated in favor of the "Use-for-ssh" attribute in the key files. What is now the correct way to configure gpg / gpg-agent to use ...
a2k42's user avatar
  • 123
25 votes
5 answers
9k views

Should I be worried about unusual SSH login attempts from unknown IP addresses?

I've been monitoring my server's SSH logs and noticed a steady stream of login attempts from unknown IP addresses, mostly from different countries. Heaps and heaps of account names are tried, and with ...
security_paranoid's user avatar
2 votes
3 answers
163 views

Should one be concerned about public keys being copied to wrong servers accidentally?

I am currently automating the setup of a web server with Ansible. My two team mates should be able to run the Ansible playbook as well. Therefore, their public keys need to be added to the ...
rmoestl's user avatar
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1 answer
101 views

Unique SSH Keys With Identical Password?

I'm a one man shop. All I care about is having my workstations and server stolen. I plan on running a couple dozen VMs on my server, mostly Linux. Question is, obviously having unique passwords for ...
Xoteric's user avatar
0 votes
1 answer
229 views

Ssh ciphers order list based on security

hmac-sha256, [email protected], hmac-sha2-256, [email protected], hmac-sha512, [email protected], hmac-sha2-512, [email protected] Can someone help in ordering the above ...
user74320's user avatar
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Does using a VPN to allow ssh connections provide better security, especially after seeing how CVE-2024-3094 (XZ backdoor) is done?

For my own (public) servers, is it considered a good idea to only allow ssh connections from VPN connections (OpenVPN, Wireguard or otherwise), to mitigate any possible attacks in the future on ssh? ...
The Quantum Physicist's user avatar
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ssh-keygen fido2 keys without password [duplicate]

ssh-keygen -t ed25519-sk -O resident -C "yubikey-fido1 My understanding is that I should be able to generate openssh keys with fido2 without password and require touch-only. While that opens up ...
cen's user avatar
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2 votes
1 answer
205 views

Openpubkey SSH workflow details

Currently looking into OpenPubKey and more specifically into OpenPubkey SSH: https://github.com/openpubkey/openpubkey https://docs.bastionzero.com/openpubkey-ssh Terminology: OPK => OpenPubkey ...
ieggel's user avatar
  • 225
4 votes
2 answers
783 views

securely tunneling through a MITM proxy

I am wondering if there is a practical way to establish a secure, encrypted network connection through an MITM proxy given the ability to communicate secrets out-of-band with a second, external proxy. ...
Aryeh Leib Taurog's user avatar
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1 answer
183 views

Port knocking through NAT for self-hosted server

I decided to move to self-hosting because it is cheaper. What I want to host: My personal website Some apps for fun Maybe later a Honeypot I have my old laptop acting as the main host. It has Ubuntu ...
rudeus123's user avatar
0 votes
0 answers
135 views

Is using OpenSSH Authentication Agent on Windows 11 a secure practice?

I use a passphrase on my SSH key used for git. I wanted to be able to use the same git for a few scripts I run to clone/pull a bunch of my repos. I discovered that I don't have to repeatedly enter my ...
Scorb's user avatar
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116 views

Security on home system - ssh keys etc

I use two computers every day, my home server which is a desktop system and my laptop. Both systems run xubuntu and, being mostly a command line user, I use ssh to connect between the systems, to ...
Chris Green's user avatar
0 votes
0 answers
151 views

How safe is it to run an un unpatched, internet-exposed OpenSSH service?

There have recently been several reported security issues with OpenSSH (Terrapin, double-frees, remote execution, X11 forwarding vulnerabilities..). How safe is it for a server to expose OpenSSH (...
benjimin's user avatar
  • 165
2 votes
3 answers
223 views

If I control both sides of a connection, is there any reason to support alternate cipher suites?

If I have a system where I have 100% control over the client operating system and the server operating system, is there any use case for enabling more than one cipher suite (or any of the options that ...
Peter Turner's user avatar
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0 answers
98 views

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 ...
Kevin Meier's user avatar
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110 views

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 ...
Sam Z's user avatar
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0 votes
0 answers
118 views

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 ...
Silas's user avatar
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1 vote
2 answers
406 views

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?
OLEGSHA's user avatar
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0 answers
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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 (...
F. Hauri  - Give Up GitHub's user avatar
0 votes
0 answers
131 views

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 ...
Simon Huenecke's user avatar
1 vote
1 answer
370 views

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 ...
round.robin's user avatar
1 vote
2 answers
4k views

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-...
Jhon Laurence's user avatar
4 votes
1 answer
763 views

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 ...
LetMeSOThat4U's user avatar
0 votes
1 answer
385 views

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 ...
Blue Herring's user avatar
1 vote
2 answers
137 views

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 ...
user228062's user avatar
1 vote
1 answer
2k views

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 ...
rocky_alpine's user avatar
0 votes
2 answers
153 views

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 ...
Hannes's user avatar
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0 votes
2 answers
378 views

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 ...
user129393192's user avatar
1 vote
1 answer
274 views

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 ...
Mike McManus's user avatar
  • 1,355
1 vote
1 answer
222 views

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 ...
Akam's user avatar
  • 1,357
0 votes
1 answer
468 views

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 ...
mpr's user avatar
  • 3
2 votes
3 answers
305 views

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 ...
ojo's user avatar
  • 39
7 votes
1 answer
9k views

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 ...
Leonardo's user avatar
  • 173
1 vote
0 answers
1k views

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 ...
Saul Goodman's user avatar
0 votes
1 answer
124 views

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 ...
Jachdich's user avatar
  • 103
4 votes
1 answer
545 views

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 ...
angryserver's user avatar
4 votes
3 answers
218 views

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 ...
David Boshton's user avatar
1 vote
1 answer
488 views

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 ...
basse's user avatar
  • 111
1 vote
1 answer
10k views

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 : ...
Cophmat's user avatar
  • 11
1 vote
0 answers
228 views

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 ...
Wesley Jones's user avatar
1 vote
0 answers
2k views

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 ...
UndercoverDog's user avatar
1 vote
2 answers
1k views

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 ...
PatS's user avatar
  • 121
1 vote
2 answers
956 views

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 ...
mgiuffrida's user avatar
2 votes
1 answer
184 views

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 ...
Cathan's user avatar
  • 21
4 votes
2 answers
1k views

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 ...
Tom Hale's user avatar
  • 3,055
0 votes
1 answer
166 views

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, ...
Okoba's user avatar
  • 17

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