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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Is there a security benefit to giving an SSH key a passphrase when using certificates?

https://goteleport.com/blog/how-to-ssh-properly/ I'm following this guide on setting up SSH certificates, and it says to NOT put a passphrase on keys, or that it's "my choice" whether to do ...
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What are possible implications of ignoring the ssh host key warning?

With password authentication you're basically giving your password to the attacker. At least that is my understanding. What about public key authentication? I hear that a private key never leaves your ...
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"Mutuality" of public key authentication

I'm a newbie when it comes to cryptographic security, but there's something I'm not quite getting concerning the "mutual" aspect of public key authentication. Say you have a client X, and ...
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How can I see the details of Total banned of Fail2Ban? [migrated]

I installed Fail2Ban as IDS in my server /home/bheng/app/(master*) # fail2ban-client status sshd root@b-world Status for the jail: sshd |- Filter | |...
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Any known SSH attacks/vulnerabilities other than brute force, dictionary attacks and compromising keys?

I am looking for attacks over Tor that can be applied to a server running SSH. I have been looking at SSH.com, IEEE papers, SpringerLink papers/books, etc. but so far I have only found that the ...
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SSH Agent Forwarding - What are the best practices and current security issues?

Using agent forwarding comes with a risk, but stored private keys can also abused if the attacker has compromised the remote machine. In this thread I want to discuss, if agent forwarding is save to ...
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How to detect weak SSH keys affected by CVE-2021-41117

Recently, GitLab[1] and GitKraken[2] notified users about a vulnerability in GitKraken version v in range 7.6.0<=v<=8.0.0. Those versions are affected by CVE-2021-41117[3] and therefore, ...
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SSH: MITM attack during fingerprint verification?

The first time I connect via SSH, a "fingerprint" appears. How can I be sure that it belongs to my server/router/etc. and has not been tampered with by a fraudster (MITM)? For example, for ...
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How does chmod 600 to private ssh keys make them secure? What is the "minimum" accepted to connect via SSH?

Just finished a simple local file inclusion challenge and I wanted to make sure if I understood the issues around permissions and SSH keys correctly: -We set private ssh keys to 600 so only the user ...
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Configure the Metasploit SSH client to support `aes256-cbc`

I am trying to set up a vulnerable machine running freeSSHd 1.2.6. The Metasploit exploit module fails with the following error: Server encryption_client preferences: aes128-cbc,3des-cbc,blowfish-cbc,...
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can an SSH session be initiated with a public key

I am able to SSH into an Embedded Linux device remotely using a private key with the following command as example (where id_rsa is the private key file): ssh -i id_rsa root@192.168.30.199 This will ...
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Secure way to set up GitHub repository in shared remote machine

I have access to a shared remote machine to execute code and store data, accessible through SSH from my local machine, but I do not have root privileges there. The remote is shared among many users. I ...
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Sharing Yubikey via SSH

I have a MacBook which has a Yubikey. I usually don't use my MacBook for any development. I use a remote Linux server. I would like to sign my commits with Yubikey instead of a gpg key. Can I share my ...
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Is it possible somebody could have edited my known_hosts file to connect to malicious servers?

Sorry if this question is stupid or doesn't make sense. What led me to ask this is that I noticed my known_hosts file has many (15) lines and I'm not sure why; I didn't think I had connected to this ...
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Disable everything but a hidden command for root access

linux security and root access question.... I'm setting up a server that has a validator node running on it for a blockchain. I was trying to harden the security of my server. I set up ufw for all ...
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Percent-encoding in WinSCP in SFTP password, why?

I recently discovered the problem with Percent-encoding. It makes perfectly sense when we are dealing with such problem in a browser scenario. But I don't get why a software like WinSCP can be ...
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682 views

Why are rsa-sha2-512 and rsa-sha2-256 supported but not reported by ssh -Q key?

Running on macOS, I see these available key algorithms: $ ssh -V OpenSSH_8.1p1, LibreSSL 2.7.3 $ ssh -Q key ssh-ed25519 ssh-ed25519-cert-v01@openssh.com ssh-rsa ssh-dss ecdsa-sha2-nistp256 ecdsa-sha2-...
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is plain SOCKS5 secure? [duplicate]

I'm confused about Socks5. Some pages claim that Socks5 is protected between you and the server, but not encrypted. How can that be safe? ..and some pages say you need an SSH tunnel for Socks5. ...
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Is there a reason to renew host SSH certificates?

tl;dr: In certificate based SSH authorization, is there any benefit to keeping host certificates lifespan short? Do you gain anything by renewing them periodically? Full Story Recently I have been ...
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Can VPN steal ssh password?

Is it possible leak ssh password while using vpn ? I mean not ssh key but password! Is it secure to connect via ssh(with plain password) while using vpn (like protonVPN or NordVPN). Thanks.
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Are there any negative consequences if you change your ssh config for a host with `UpdateHostKeys no`?

I recently came across a question on stackoverflow.com regarding gitlab.com and ssh config. The solution apparently is to update your ssh config with the following: Host gitlab.com UpdateHostKeys ...
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Why does Lightsail require the server's private key to connect via SFTP?

I am still learning about SSH, SFTP and private/public keys. My elementary understanding of keys is that the private key should remain on the machine it was generated on and never be shared. I have a ...
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Can a running SSH connection to a rootkit infected VPS be used to attack the remote client?

If a VPS running Debian 10 Xfce as a cloud desktop has been rootkit infected and there is an ongoing SSH connection with X2Go from a client to manage this server, is it possible for an attacker on the ...
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is MITM attack possible when we verify only the jump host's fingerprint (host key)?

I am connecting to remote hosts via jump host where I verify only the jump host's host key, but turn off host key verification for the target hosts. the ssh command arguments look like this: -o ...
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Is it possible to disable login via password in ssh? [duplicate]

I had an idea to secure my system better when someone tries to ssh into my machine and that had to do with ssh keys. When logging in with ssh, you are prompted with a password that, if correct, gives ...
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What's the point of connecting to another machine with SSH to crack a password?

If anyone has heard of Ippsec and watched his videos, you'll see that when he extracts a password hash from a machine, he doesn't crack it in his own computer, rather, he uses SSH to connect to his ...
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Connect to VPN Server with SSH from computer connected to the VPN itself?

I think I already responded this question to me (doing some experiments). However, I wanted to ask just for further confirmation. Context: I have an OpenVPN server installed on an AWS EC2 instance. ...
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Can you obtain the passphrase of an encrypted SSH key, given the unencrypted key?

Imagine you get hold of someone's private SSH key, which is encrypted. Now imagine you also get hold of the unencrypted key (e.g., because some SSH client stores it after decryption). Can you ...
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SSH Tunnel HTTP Security

I think I have this set up right, but I'd appreciate a sanity-check and any info on best practices that I should be using for creating SSH tunnels to my home network while traveling. Home network: ...
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372 views

How does ed25519-sk actually works?

My google-foo failed me as most "how it works" sections related to fido are very... let's say... consumer-oriented. So openssh supports U2F natively when using the appropriate elliptic-curve-...
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OpenSSH authorized_keys options for securely tunneling to a database

I would like to allow people to tunnel to either db1.example.net or db2.example.net based on their SSH public keys via a bastion server bastion.example.net. What SSHD options should I add to the ~/....
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Is getting server host key with ssh-keyscan secure?

I am trying to establish SSH connection to a server through a program. As a pre-requisite to be able to do so, I am getting the publicly available server host key using ssh-keyscan <hostname> ...
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1answer
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Is it fine to save contact information on a ssh sever and is it secure?

My mom wants to find a way to store information securely and host it remotely and wants to host our own mini-server on a Raspberry Pi that'll have contact information of the customers. My sister said ...
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1answer
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How exactly is RSA used in SSH [duplicate]

I can find oodles of websites that tell me the server retains the public key and the client retains the private key. But nothing on how the client authenticates to the server and - perhaps - how the ...
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Why are SSH MITM tools able to read and modify data?

At my university, we are learning how to use SSH for server administration. We learned that SSH is secure, but there are some tools that allow man-in-the-middle attacks on SSH. How can such tools ...
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Should I backup a GPG key used for Authentication?

Regarding backups (escrows) of GPG (OpenPGP compliant) keys, I seem to understand that (E)ncryption keys need to be backed up, to prevent data loss, and that (S)igning keys should not be backed up, ...
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How can you attack or redirect the client from the server over an RDP or SSH conneciton? [closed]

I have a penetration testing scenario where I am on the network with two machines, Machine A and Machine B. I have complete control over Machine B and am trying to leverage that to get access to ...
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Preventing MITM for a new SSH daemon

Supposed I have a number of HTTPS servers on different networks, would it be safe enough to use them together to verify a new SSH daemon's public key? i.e. if they all return the same fingerprint, is ...
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Serverside SSH security best practices

In light of the 2006 Debian OpenSSL fiasco, it seems prudent to take additional precautions as part of a "defense in depth" strategy against future possible vendorside-introduced ssh ...
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IPSec MTU DDos attack

I have this configuration: HOST-A <---> GAT-A <---> MiTM <---> GAT-B <---> HOST-B I'm doing a security project on MTU-IPsec vulnerabilities and following this guide of Hal-...
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1answer
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SSH and PCI on Insecure, Dirty Side

Does current PCI code require SSH connections be restricted to enumerated (specific) client IP addresses on the unsecure, dirty side? Isn't that outside the scope of the PCI code?
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ssh login attempts still showing up even with password login disabled? [duplicate]

I switched all my servers to ssh publickey login and disabled password login about a week ago (root login IS still enabled). I also run Fail2ban and logwatch. Why is there still login attempts ...
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SSH reverse tunnels: can the intermediate server eavesdrop on an SSH session?

Suppose there are three computers: (1) my laptop, (2) a server that has a public static IP address, and (3) a Raspberry Pi behind a NAT. I connect from (1) to (3) via (2) as explained below. On the ...
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Why should we only keep the private key secret, why not the public key? [duplicate]

If I am not wrong, both private key and public key are the same since communication is possible only if both keys are matching. So, why we should only keep the private key secret, why not public key? ...
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SSH Public Key Authentication Strength Port 22 [duplicate]

Let’s say I have a server with Port 22 opened to the internet , password authentication disabled, and root remote login disabled. Only Key Authentication is enabled. If the key is tightly secured, is ...
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How to make access to a remote program without that the user has the possibility to run any Linux command?

I have an interactive program. Actually, the program can be reachable over SSH. In the .profile file, the program is launched immediately and with the interactive interface it is not possible to ...
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In an enterprise environment, should developers/maintainers be able to look at production logs by accessing the application servers?

I came across this practice, from a big company handling personal customer data, of not allowing developers/maintainers to look straight at the application logs (e.g. good old tail | grep) by ...
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What is the added security of “PermitRootLogin no” alone?

Referring to this Q&A: The setting PermitRootLogin no alone does not prevent su - after logging in as a normal user. As described in the referenced answer, there it is possible to prevent su with ...
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How roaming works with ssh private keys?

This occurred to me when looking at the security model wireguard is using. Instead of relying on users credentials and Radius authenticating central server each user has a private key used to ...
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Hydra attack ssh : The message is successful, but when using the errors

I execute the command hydra -l ubnt -p ubnt 138.255.252.193 -t 4 ssh I get the message it's successful Hydra (http://www.thc.org/thc-hydra) starting at 2021-02-22 11:32:05 [DATA] max 1 task per 1 ...

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