The SSH (“Secure Shell”) protocol is a method for secure remote login from one system to another. Sysadmins and users use a secure channel over an unsecured network in a client-server architecture format for connecting an SSH client with an SSH server. Security ssh server is an important task. There is a tool called ssh_scan from Mozilla which act as a prototype SSH configuration and policy scanner for your SSHD.
Benefits of ssh_scan
From the project home page:
- Minimal Dependancies – Uses native Ruby and BinData to do its work, no heavy dependancies.
- Not Just a Script – Implementation is portable for use in another project or for automation of tasks.
- Simple – Just point ssh_scan at an SSH service and get a JSON report of what it supports and its policy status.
- Configurable – Make your own custom policies that fit your unique policy requirements.
Install dependancies
Type the following apt-get command/apt command to install ruby and gem on Debian/Ubuntu Linux:
$ sudo apt-get install ruby gem
Sample outputs:
Install ssh_scan
Type the following command to install ssh_scan as a gem:
$ sudo gem install ssh_scan
Sample outputs:
How do I use ssh_scan?
The syntax is:
$ ssh_scan -t ip
$ ssh_scan -t server
$ ssh_scan -t server1.cyberciti.biz
For example scan a ssh server installed at 192.168.2.15, enter:
$ ssh_scan -t 192.168.2.15
Sample outputs:
I, [2017-04-25T16:12:11.019160 #32317] INFO -- : You're using the latest version of ssh_scan 0.0.19 [ { "ssh_scan_version": "0.0.19", "ip": "192.168.2.15", "port": 22, "server_banner": "SSH-2.0-OpenSSH_7.4p1 Ubuntu-10", "ssh_version": 2.0, "os": "ubuntu", "os_cpe": "o:canonical:ubuntu", "ssh_lib": "openssh", "ssh_lib_cpe": "a:openssh:openssh:7.4p1", "cookie": "82d7cc908765f03154b10d5cdf14195a", "key_algorithms": [ "curve25519-sha256", "[email protected]", "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "diffie-hellman-group-exchange-sha256", "diffie-hellman-group16-sha512", "diffie-hellman-group18-sha512", "diffie-hellman-group14-sha256", "diffie-hellman-group14-sha1" ], "server_host_key_algorithms": [ "ssh-rsa", "rsa-sha2-512", "rsa-sha2-256", "ecdsa-sha2-nistp256", "ssh-ed25519" ], "encryption_algorithms_client_to_server": [ "[email protected]", "aes128-ctr", "aes192-ctr", "aes256-ctr", "[email protected]", "[email protected]" ], "encryption_algorithms_server_to_client": [ "[email protected]", "aes128-ctr", "aes192-ctr", "aes256-ctr", "[email protected]", "[email protected]" ], "mac_algorithms_client_to_server": [ "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "hmac-sha2-256", "hmac-sha2-512", "hmac-sha1" ], "mac_algorithms_server_to_client": [ "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "[email protected]", "hmac-sha2-256", "hmac-sha2-512", "hmac-sha1" ], "compression_algorithms_client_to_server": [ "none", "[email protected]" ], "compression_algorithms_server_to_client": [ "none", "[email protected]" ], "languages_client_to_server": [ ], "languages_server_to_client": [ ], "hostname": "m6700", "auth_methods": [ "publickey", "password" ], "fingerprints": { "rsa": { "known_bad": "false", "md5": "1d:14:84:f0:c7:21:10:0e:30:d9:f9:59:6b:c3:95:97", "sha1": "70:ac:7c:2c:94:54:aa:09:f2:58:f3:48:f0:9e:f2:a0:a2:37:f1:0a", "sha256": "6d:d8:20:c6:8e:e7:db:0d:94:9d:34:66:ba:b7:9c:68:8a:ea:79:19:a6:0d:76:cc:ec:fe:82:21:68:a5:64:74" } }, "start_time": "2017-04-25 16:12:11 +0000", "end_time": "2017-04-25 16:12:11 +0000", "scan_duration_seconds": 0.118730486, "duplicate_host_key_ips": [ ], "compliance": { "policy": "Mozilla Modern", "compliant": false, "recommendations": [ "Remove these Key Exchange Algos: curve25519-sha256, diffie-hellman-group16-sha512, diffie-hellman-group18-sha512, diffie-hellman-group14-sha256, diffie-hellman-group14-sha1", "Remove these MAC Algos: [email protected], [email protected], [email protected], hmac-sha1", "Remove these Authentication Methods: password" ], "references": [ "https://wiki.mozilla.org/Security/Guidelines/OpenSSH" ] } } ]
To see all other options, enter:
$ ssh_scan -h
Sample outputs:
ssh_scan v0.0.19 (https://github.com/mozilla/ssh_scan) Usage: ssh_scan [options] -t, --target [IP/Range/Hostname] IP/Ranges/Hostname to scan -f, --file [FilePath] File Path of the file containing IP/Range/Hostnames to scan -T, --timeout [seconds] Timeout per connect after which ssh_scan gives up on the host -L, --logger [Log File Path] Enable logger -O, --from_json [FilePath] File to read JSON output from -o, --output [FilePath] File to write JSON output to -p, --port [PORT] Port (Default: 22) -P, --policy [FILE] Custom policy file (Default: Mozilla Modern) --threads [NUMBER] Number of worker threads (Default: 5) --fingerprint-db [FILE] File location of fingerprint database (Default: ./fingerprints.db) --suppress-update-status Do not check for updates -u, --unit-test [FILE] Throw appropriate exit codes based on compliance status -V [STD_LOGGING_LEVEL], --verbosity -v, --version Display just version info -h, --help Show this message Examples: ssh_scan -t 192.168.1.1 ssh_scan -t server.example.com ssh_scan -t ::1 ssh_scan -t ::1 -T 5 ssh_scan -f hosts.txt ssh_scan -o output.json ssh_scan -O output.json -o rescan_output.json ssh_scan -t 192.168.1.1 -p 22222 ssh_scan -t 192.168.1.1 -p 22222 -L output.log -V INFO ssh_scan -t 192.168.1.1 -P custom_policy.yml ssh_scan -t 192.168.1.1 --unit-test -P custom_policy.yml
How do I secure and optimize my OpenSSH server?
- OpenSSH Security Best Practices
- For providing a sane baseline policy recommendation for SSH configuration parameters see this page