Questions tagged [openssh]

A free and open implementation of the SSH communication security tools.

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1answer
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SSH Keybased authentication using Nitrokey

So I'm fairly new to more secure forms of key management, I've been used to storing my keys inside key files on my computer. Recently I wanted to try and see if I could setup SSH authentication to my ...
7
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1answer
5k 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[...]: ...
3
votes
1answer
659 views

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 ...
2
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1answer
629 views

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* ...
2
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1answer
681 views

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 ...
6
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1answer
1k views

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 ...
5
votes
1answer
5k views

Is the OpenSSH server using a fallback, hard-coded DH parameter for 2048bits?

I'm toying around with OpenSSH configs and poking at the Diffie-Hellman parameters. I'm using GDSSecurity's tool to check DH settings and this page to view other SSH settings. For funsies, I removed ...
73
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3answers
50k views

Why OpenSSH deprecated DSA keys

There was a question RSA vs. DSA for SSH authentication keys asking which key is better. Basically all answers were more in a favour of RSA over DSA but didn't really tell that DSA would be somehow ...
2
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1answer
1k views

OpenSSH < 7.0 Multiple vulnerabilities question

Nessus reports this as Critical however there are issues such as 'CVE-2015-5600' that CVE is 8.5 but Red Hat reports it as a 'Low' issue. https://access.redhat.com/security/cve/CVE-2015-5600 Reports ...
3
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1answer
441 views

Is there any information on the impact of CVE-2016-1907 (openSSH)?

I just saw the notification about CVE-2016-1907 this morning: The ssh_packet_read_poll2 function in packet.c in OpenSSH before 7.1p2 allows remote attackers to cause a denial of service (out-of-...
21
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2answers
11k views

How exploitable is the recent UseRoaming SSH vulnerability?

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-...
4
votes
1answer
31 views

Benefit of having multiple DH moduli of same length?

What is the benefit of having multiple Diffie Hellman moduli of the same length in OpenSSH's moduli file? In the distributed moduli file there are around 40 primes for each length to choose from ...
0
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2answers
234 views

Filtering safe primes for Diffie Hellman on OpenVPN

When creating Diffie Hellman parameters for OpenSSH, there's a two-step process which looks like this to generate and filter secure primes for Diffie Hellman key exchange: ssh-keygen -b 4096 -G ...
2
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2answers
498 views

How much entropy should passphrases for encrypting ssh keys have?

When one generates keys using ssh-keygen one gets prompted for a passphrase to encrypt the generated key with. How strong should such a passphrase be, entropywise, to withstand a full-blown brute-...
4
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1answer
916 views

Is the ssh-copy-id command secure?

I have 2 Ubuntu 14.04 servers with openssh-server installed on both. I've set up key-based authentication using RSA keys, without passphrase, so that I can run automated backup scripts, to a remote ...
5
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1answer
1k views

Does RekeyLimit property in sshd_config enforce re-keying / key re-exchange?

I have set the RekeyLimit property in sshd_config and tried to perform a SSH. However, I could not see rekeying happening in the verbose logs, all I see is the log message below at the start of the ...
1
vote
1answer
700 views

Use HSPD-12 (PIV) Keys for SSH

Can I use the on-board key generated keys on the HSPD-12 card as openssh keys? If so, how?
4
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3answers
2k views

Docker X11 Forwarding Security

I am currently running a Docker container with a program with a GUI forwarded over SSH (using X forwarding over OpenSSH). The virtualized server has X11Forwarding enabled and I can connect to it from ...
0
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1answer
1k views

Generate RSA2 key in OpenSSH format in windows

I have to generate a key, RSA v2 in OpenSSH format. I am a bit confused. I am trying to generate it using Putty key generator. There I see an option SSH2-RSA and SSH1-RSA. So is SSH2-RSA the RSA2 key ...
5
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2answers
897 views

Does changing /etc/ssh/moduli impact previously generated keys?

My company does a lot of automated file transfers over SSH/sftp with banks, etc. A recent SSH upgrade on a server dropped support for the old/weak diffie-helman-group1-sha1 key exchange protocol in ...
11
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1answer
3k views

Are there any risks associated with SSH agent forwarding?

I just realized that I need SSH agent forwarding in order to push to one Git server that then forwards the commits to Github.com. I never used SSH agent forwarding and don't understand the security ...
4
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2answers
166 views

Is it safe to expose a logging socket endpoint in a chrooted environment?

I'm trying to set up a file transfer server, which needs to be secured and logged. FTP was suggested, but that feels outdated so I automatically translated that to SFTP (OpenSSH) in my head. Using ...
7
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2answers
267 views

System breach or OpenSSH glitch?

The system runs a SSH daemon, and a nginx web server, both ports being open to the internet. We are part of a university so our ports are forwarded from the main router to the intranet. At about 19:...
1
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2answers
235 views

ssh/scp from server to server — set permissions (no root)

I have access as a regular user (not as root) to two servers. Server A is accessible via ssh with a username and password, Server B can only be accessed using a keycard and pin. I need to set up a ...
1
vote
1answer
2k views

Create Public Key using OpenSSL instead of PuTTYgen for PKCS#8

I'm trying to create a public key pair for ssh-rsa authentication. If I'm using puttygen.exe, the "OpenSSH authorized_keys file" string looks like this: "ssh-rsa AAAAB3 ... 6yIK9Nbw== rsa-key-...
4
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1answer
4k views

LogJam hardening OpenSSH and testing it [duplicate]

I would like to harden my OpenSSH (clientsite) after the LogJam attack. I read this article https://weakdh.org/sysadmin.html and there is one paragraph, which says how to do that. Is this enough and ...
1
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1answer
718 views

Strange SECCOMP entries for sshd in audit log

I've posted this over at ServerFault but haven't received a response over there. I'm not a security professional, but I'm curious as to what kind of attack this might be and how the attackers might be ...
2
votes
1answer
1k views

Are OpenSSH vs OpenSSL public key format names mismatched?

I generated a key pair vis OpenSSH and later wanted to generate PEM encoded public key. I noticed that generated public key differs when generated by OpenSSH vs OpenSSL when using same format name (...
6
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1answer
162 views

What are 'screened' DH groups?

Currently it's recommended to do something about the contents of /etc/ssh/moduli. I've seen two ways: to strip all moduli of less than 2047 bytes size from the file. to recreate them using ssh-keygen....
16
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1answer
7k views

Is it considered worth it to replace OpenSSH's moduli file?

Consequences of tampered /etc/ssh/moduli describes a possible risk if the moduli file for an OpenSSH server has been tampered with. Taking the logic a step further, is there any concern with the ...

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