Questions tagged [openssh]
A free and open implementation of the SSH communication security tools.
119
questions
0
votes
2answers
76 views
How to accept only user identity keys of type ed25519 on OpenSSH Linux server?
I want to force all users to use only ed25519 type keys when logging in via SSH / SFTP to a Linux server which is running a recent version* of OpenSSH.
Some general reasons for putting controls on ...
4
votes
1answer
67 views
Does `ssh-keyscan` verify the legitimacy of the host(s) it scans?
There are tutorials on the web, such as this one: https://blog.oddbit.com/post/2019-02-24-docker-build-learns-about-secr/
They show you sample code to run ssh-keyscan in an automated manner so that ...
0
votes
1answer
30 views
changing defaults when generating new SSH server keys
On Debian, I can generate new SSH server keys:
rm /etc/ssh/ssh_host_*
dpkg-reconfigure openssh-server
but that will generate the keys with default values, ie 2048 RSA key.
What is happening under ...
0
votes
0answers
70 views
SSH (ssh_auth_list) authentication failing from windows to linux
Bit new in ssh and have an issue in understanding. I got a code which uses ssh_auth_list routine as below.
method = ssh_auth_list(session);
printf(" %d " , method);
I am using a ssh library and when ...
1
vote
2answers
244 views
Convert ECDSA keys (PEM, OpenSSH)
To work with ECDSA keys I am using the python-ecdsa library. Unfortunately this library can not process keyfiles properly if they are provided in the OpenSSH format. Instead I generate them in the PEM ...
0
votes
0answers
76 views
How secure is passwordless and keyless SSH login on 127.0.0.1 only, over a secure authenticated tunnel?
I want to use CA signed SSH keys (that would be rotated frequently and have short expiry, ideally centrally managed, all that great stuff). Unfortunately, most of windows GUI tools, such as WinSCP or ...
0
votes
0answers
78 views
SSH AUTH : sekey vs yubikey vs ssh-keygen
I've been pondering/hacking/experimenting/using/misusing and am torn/puzzled over this for the past month or so;
Which of these methods should prove themselves more secure/least susceptible to be ...
3
votes
1answer
114 views
Exposure of /etc/ssh, risks?
I accidentally exposed the keys in /etc/ssh
What is the risk?
I think it will allow someone to impersonate the server and conduct MITM.
Will it let someone SSH into the server? I think not because ...
0
votes
0answers
48 views
Sufficient to only require 2FA for su elevation?
I have a small web-facing server on my home network. It is headless, and the only way to log in is to ssh with pubkey authentication from within the local network.
I wanted to turn on a 2FA ...
0
votes
0answers
45 views
Convert openssl private key to openssh private key [duplicate]
I have an openssl format private key that i need to use as a host key for openssh connection.How can i convert the openssl format private key to openssh formatted private key using ssh-keygen.I have ...
1
vote
0answers
62 views
Bruteforcing via port 88 on MacOS
Macos has open port 88 by default. Is it possible to check validity of the password via this port from Linux and how?
If the vncserver is active, it is possible to know also the username (by ...
2
votes
1answer
183 views
Can a SSH jump host act as MITM?
Let's say, for example, a company has a "centralised" SSH bastion/jump host on an untrusted server (e.g. a virtual machine in "the cloud").
Meanwhile the corporate/customer/whatever network(s) have ...
4
votes
1answer
121 views
How were attackers able to login to the Apache Foundation's infrastructure over ssh with passwords? (2010)
SSH passwords should not have been enabled for login over the Internet. Although the Infrastructure Team had attempted to configure the sshd daemon to disable password-based logins, having UsePAM yes ...
1
vote
1answer
660 views
Loading a passphrase-protected private SSH key from a file with the cryptography Python module
I am trying to load a passphrase-protected private SSH key from a file using the cryptography Python module. However, I'm not exactly sure how to proceed. The following yields a Crypto.Util.Padding....
1
vote
1answer
317 views
How do I determine if an existing SSH private key is secure?
For an ordinary user, how would I verify that a private key file was generated using reasonably secure algorithms? In response to things like allegedly insecure ssh-keygen defaults.
1
vote
2answers
87 views
Possible to get sshd (openssh) to log the public key of failed key based login attempts?
As I understand sshd (openssh in my case) typically does/may log the fingerprint/hash of the public key of incoming connections which are attempting to authenticate via key.
What I'm looking for is ...
3
votes
0answers
83 views
Could a running SSH server somehow fool connected SSH client to create a reverse port forward?
Let's be extra paranoid and assume that the SSH server my client is connected to, was "enhanced" so that every SSH client that establishes an connection with it, will be tricked into thinking that it ...
0
votes
1answer
2k views
Checking if an RSA private key is passphrase protected
I have generated an RSA key-pair on a computer, and I want to check if the RSA private key is encrypted (protected) with a passphrase.
Note that the problem is not that I forgot the passphrase, but ...
5
votes
2answers
548 views
From FTP to SSH
Currently, I am doing a penetration testing laboratory with a server with the following services:
Nmap scan report for 10.0.11.125
Host is up (1.3s latency).
Not shown: 998 closed ports
PORT STATE ...
2
votes
3answers
713 views
Are mkpasswd SHA512 hashes secure for the public?
I am no crypto expert in any way so please bear with me if my question is kind of stupid.
We use OpenSSH key pairs on a regular basis and due to the asymmetric nature of key pairs, as far as I ...
2
votes
2answers
1k views
For CA-signed ssh keys, how to see various attributes: principals, identity, serial number, options, validity time, etc
I am looking to implement access controls through CA-signed public ssh keys, as described in the article Scalable and secure access with SSH.
I am trying to conceive how our security team will manage ...
4
votes
1answer
430 views
OpenSSH-server: Are there any security implications and/or value of/for 'TCPKeepAlive yes'
I have read a degree of mixed reports on the security implications and/or value of allowing TCPKeepAlive yes in /etc/ssh/sshd_config (for OpenSSH-server). Anything definitive on the security best ...
1
vote
1answer
186 views
Does OpenSSH use padding of random lengths?
According to the end of RFC 4253 § 6, the random padding introduced to each SSH packet is an arbitrary multiple of 8. It mentions that random padding lengths can mitigate traffic analysis:
Note ...
5
votes
2answers
9k views
Any Alternative to Ngrok for constant Connection? [closed]
Im trying to build RAT to test on my computer. I use ngrok for hacking on WAN. But ngrok has a problem of changing its subdomain once the connection is reset. So, I cant use ngrok for hacking over WAN....
0
votes
2answers
65 views
Concept using ssh to create dynamic firewall. Good or Bad idea?
The Goal
Create a secure process to open a firewall port on a server (on demand), start a listening server, and ultimately close the firewall port. This would improve security by not always having a ...
-2
votes
1answer
103 views
What is the most private option for 2FA with OpenSSH?
When I watch the logs on my server there are always many hundred IP addresses with failed ssh logins.
Because fail2ban only slows the attack process down, I decided that I need another solution. ...
2
votes
0answers
131 views
Why does the openssh-server not use GCM by default?
Well the question is as simple as that . Because I recently noticed that the openssh-server uses AES-CTR for the symmetric encryption and I wondered why ?
From what I heared AES-CTR is a block cipher ...
4
votes
0answers
1k views
What is the general approach to create FIPS compliant SSH?
Please bear in mind that I have no cyber-security background at all, but have been tasked by my company with making certain applications on our platform FIPS-compliant.
From what I've discussed with ...
6
votes
2answers
12k views
Is there a list of weak SSH ciphers?
Is there a site, which provides a list of weak cipher suites for (Open-)SSH? I know for example that arcfour is not recommended, but there is a whole list of other cipher suites offered, where I am ...
1
vote
1answer
590 views
what are the disadvantages of running SSH daemon without root?
Is there any risk in running ssh daemon with no root privilege using this method: how-can-i-make-this-daemon-init-run-as-a-non-root-user?
Debian Developer's Best Practices for OS Security says the ...
1
vote
1answer
158 views
SSH Proxy vs VPN Killswitch
This might be complete nonsense but I've heard people talking about so I'm interested to see if it's valid: I've heard people saying that SOCKS and SSH are more secure/private than a VPN because they ...
4
votes
1answer
362 views
SSH and man-in-the-middle
Assume the following scenario and please correct me if I am wrong somewhere:
There is a client and there is an SSH server that the client connects to. There is also a man-in-the-middle (MIM) which is ...
3
votes
1answer
433 views
Why are SSH host keys stored un-encrypted?
Do we have any standard way to encrypt SSH host keys (like /etc/ssh/ssh_host_rsa_key)? If not, why is it stored in plaintext? Isn't it sensitive information?
2
votes
1answer
469 views
Limit on modulus lines in OpenSSH /etc/ssh/moduli file?
I understand that OpenSSH server looks in /etc/ssh/moduli and picks a modulus at random for each Diffie-Hellman group exchange. What I am wondering is whether there is a practical limit on how many ...
0
votes
1answer
53 views
Negative consequences of forced encryption of unencrypted secvices
Are there any negative consequences to encrypting an unencrypted service/protocol like FTP, VNC, telnet, and so on by using forced encryption like ssh tunneling or OpenVPN tunnels?
2
votes
3answers
323 views
How to prevent sharing SSH private keys by email
Is it possible to prevent the sharing of SSH private keys over email (Outlook, in particular), both within and outside of the organisation?
4
votes
2answers
317 views
Security benefit of hardware backed host keys for OpenSSH
There was recently a "two for the price of one" deal on the Yubikey 4 and now I have too many of them.
This got me thinking about things to do with them, more or less useful. Of course I already use ...
2
votes
1answer
56 views
Are the keys generated by ssh-keygen only used in authentication?
After reading SSH Passwordless Login Using SSH Keygen in 5 Easy Steps, I come across the question: Are the keys generated by ssh-keygen only used in login authentication? I mean if I want to modify ...
1
vote
0answers
214 views
tools for testing ssh packets size [closed]
I need to test maximum-packet-size for SSH protocol. Would be grateful for information on possible tools that can be used for this. What I specifically need is the possibility to indicate packet ...
5
votes
3answers
12k views
Copy SSH Public Key from Windows to Ubuntu
I am trying to get my ssh public key from my windows client to ubuntu host, but I have no idea how to. I tried to find the authorized_keys file, but had zero success. ssh-copy-id command did not work ...
5
votes
3answers
3k views
How secure is ssh key-based authentication
I have a newly installed (and updated) Centos 7 server I use for testing.
I implemented RSA key based authentication for ssh and set PermitRootLogin to without-password
When I logged on this morning ...
1
vote
1answer
144 views
How to force openssh client to require both SSH certificate and SSHFP record?
Securely authenticate SSH hosts
I have successfully used both OpenSSH Certificates and SSHFP to authenticate hosts when connecting to servers using SSH. But I fail to find a way to require the ...
0
votes
1answer
968 views
Pentest - how to further exploit LFI / ssh / mysql
I am conducting a pentest where I got stuck on the following problem:
I found a LFI in a php file. I am trying to exploit it and to get a shell or any further usage out of it but until now without ...
0
votes
2answers
168 views
What is the risk if I don't have a passphrase associated with CA private key?
I understand that it is better to use a passphrase for SSH private keys so that even if someone accesses your machine, they can't simply SSH into a protected machine using your keys.
My question is ...
2
votes
1answer
541 views
What does ssh-keygen's -a option really mean?
I discovered the newer OpenSSH format for storing SSH private keys (ssh-keygen -o) uses bcrypt to generate the symmetric key to encrypt the private key. I understand that the -a option is used to ...
1
vote
0answers
456 views
test SSH private key from STDIN
I recently re-encrypted my SSH private key to use the new OpenSSH format with lots of KDF rounds (-o -a 200) (takes about 2 seconds to run on my CPU). Unfortunately, I mistyped my passphrase in ...
0
votes
1answer
237 views
Is MIT Kerberos supposed to ask for a password when authenticating to SSH?
According to my understanding of Kerberos, a client is supposed to only enter its password once for obtaining the TGT from the Kerberos server and the authentication against the web services (f.e. SSH,...
1
vote
1answer
135 views
What are the security implications of enabling anonymous root/sudo access with sshd on a local guest VM?
Let's say that on my personal computer, I host a VM I use to do software development. My personal computer is connected to the internet and running Ubuntu 16.04 and my guest is CentOS 7.
I don't want ...
1
vote
1answer
651 views
SSH ED25519 Key Extract pk (32 bit)
I am playing around with ssh keys with ED25519.
I have seen a couple of libraries playing with generating the public/private key pair. Another parsing the openssh private key to get the key, but the ...
1
vote
0answers
545 views
Ssh and fips mode
I am working on a networking device that needs to meet fips 140-2 level 2. ( runs on Ubuntu )
As for ssh, is it enough to limit the ciphers to those "allowed" by fips or should we patch openssh to ...
