ssh_scan – Verifies Your SSH Server Configuration and Policy in Linux

ssh_scan is an easy-to-use prototype SSH configuration and policy scanner for Linux and UNIX servers, inspired by Mozilla OpenSSH Security Guide, which provides a reasonable baseline policy recommendation for SSH configuration parameters such as Ciphers, MACs, and KexAlgos and much more.

It has some of the following benefits:

  • It has minimal dependencies, ssh_scan only employs native Ruby and BinData to do its work, no heavy dependencies.
  • It’s portable, you can use ssh_scan in another project or for automation of tasks.
  • It’s easy to use, simply point it at an SSH service and get a JSON report of what it supports and it’s policy status.
  • It’s also configurable, you can create your own custom policies that fit your specific policy requirements.

Suggested Read: How to Install and Configure OpenSSH Server in Linux

How to Install ssh_scan in Linux

There are three ways you can install ssh_scan and they are:

To install and run as a gem, type:

----------- On Debian/Ubuntu ----------- 
$ sudo apt-get install ruby gem
$ sudo gem install ssh_scan

----------- On CentOS/RHEL ----------- 
# yum install ruby rubygem
# gem install ssh_scan

To run from a docker container, type:

# docker pull mozilla/ssh_scan
# docker run -it mozilla/ssh_scan /app/bin/ssh_scan -t github.com

To install and run from source, type:

# git clone https://github.com/mozilla/ssh_scan.git
# cd ssh_scan
# gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
# curl -sSL https://get.rvm.io | bash -s stable
# rvm install 2.3.1
# rvm use 2.3.1
# gem install bundler
# bundle install
# ./bin/ssh_scan

How to Use ssh_scan in Linux

The syntax for using ssh_scan is as follows:

$ ssh_scan -t ip-address
$ ssh_scan -t server-hostname

For example to scan SSH configs and policy of server 92.168.43.198, enter:

$ ssh_scan -t 192.168.43.198

Note you can also pass a [IP/Range/Hostname] to the -t option as shown in the options below:

$ ssh_scan -t 192.168.43.198,200,205
$ ssh_scan -t test.tecmint.lan
Sample Output
I, [2017-05-09T10:36:17.913644 #7145]  INFO -- : You're using the latest version of ssh_scan 0.0.19
[
  {
    "ssh_scan_version": "0.0.19",
    "ip": "192.168.43.198",
    "port": 22,
    "server_banner": "SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.1",
    "ssh_version": 2.0,
    "os": "ubuntu",
    "os_cpe": "o:canonical:ubuntu:16.04",
    "ssh_lib": "openssh",
    "ssh_lib_cpe": "a:openssh:openssh:7.2p2",
    "cookie": "68b17bcca652eeaf153ed18877770a38",
    "key_algorithms": [
      "[email protected]",
      "ecdh-sha2-nistp256",
      "ecdh-sha2-nistp384",
      "ecdh-sha2-nistp521",
      "diffie-hellman-group-exchange-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]",
      "umac-1[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": "tecmint",
    "auth_methods": [
      "publickey",
      "password"
    ],
    "fingerprints": {
      "rsa": {
        "known_bad": "false",
        "md5": "0e:d0:d7:11:f0:9b:f8:33:9c:ab:26:77:e5:66:9e:f4",
        "sha1": "fc:8d:d5:a1:bf:52:48:a6:7e:f9:a6:2f:af:ca:e2:f0:3a:9a:b7:fa",
        "sha256": "ff:00:b4:a4:40:05:19:27:7c:33:aa:db:a6:96:32:88:8e:bf:05:a1:81:c0:a4:a8:16:01:01:0b:20:37:81:11"
      }
    },
    "start_time": "2017-05-09 10:36:17 +0300",
    "end_time": "2017-05-09 10:36:18 +0300",
    "scan_duration_seconds": 0.221573169,
    "duplicate_host_key_ips": [

    ],
    "compliance": {
      "policy": "Mozilla Modern",
      "compliant": false,
      "recommendations": [
        "Remove these Key Exchange Algos: 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"
      ]
    }
  }
]

You can use -p to specify a different port, -L to enable the logger and -V to define the verbosity level as shown below:

$ ssh_scan -t 192.168.43.198 -p 22222 -L ssh-scan.log -V INFO

Additionally, use a custom policy file (default is Mozilla Modern) with the -P or --policy [FILE] like so:

$ ssh_scan -t 192.168.43.198 -L ssh-scan.log -V INFO -P /path/to/custom/policy/file

Type this to view all ssh_scan usage options and more examples:

$ ssh_scan -h
Sample Output
ssh_scan v0.0.17 (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

Check out some useful artilces on SSH Server:

  1. SSH Passwordless Login Using SSH Keygen in 5 Easy Steps
  2. 5 Best Practices to Secure SSH Server
  3. Restrict SSH User Access to Certain Directory Using Chrooted Jail
  4. How to Configure Custom SSH Connections to Simplify Remote Access

For more details visit ssh_scan Github repository: https://github.com/mozilla/ssh_scan

In this article, we showed you how to set up and use ssh_scan in Linux. Do you know of any similar tools out there? Let us know via the feedback form below, including any other thoughts concerning this guide.

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Aaron Kili

Aaron Kili is a Linux and F.O.S.S enthusiast, an upcoming Linux SysAdmin, web developer, and currently a content creator for TecMint who loves working with computers and strongly believes in sharing knowledge.

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