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How to remotely verify SSH service configuration and policy through ssh_scan

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Release: 2024-01-05 23:12:15
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Introduction ssh_scan is an easy-to-use SSH service parameter configuration and policy scanner program for Linux and UNIX servers. Its ideas come from the Mozilla OpenSSH Security Guide. This guide provides a reliable security for SSH service parameter configuration. Recommendations for policy baselines, such as encryption algorithms (Ciphers), message authentication information code algorithms (MAC), key exchange algorithms (KexAlgos) and others.

How to remotely verify SSH service configuration and policy through ssh_scan

ssh_scan has the following benefits:

  • Its dependencies are minimized, ssh_scan only introduces local Ruby and BinData to perform its work, without too many dependencies.
  • It is portable, you can use ssh_scan in other projects or use it for automated tasks.
  • It is easy to use, simply point it to an SSH service and get a JSON-formatted report of the options and policy status supported by the service.
  • It is also easy to configure, so you can create a strategy that suits your strategic needs.

Recommended reading: How to install and configure the OpenSSH service on Linux

How to install ssh_scan on Linux

There are three ways to install ssh_scan:

Use Ruby gem to install and run, as follows:

----------- 在 Debian/Ubuntu ----------- 
$ sudo apt-get install ruby gem
$ sudo gem install ssh_scan
----------- 在 CentOS/RHEL ----------- 
# yum install ruby rubygem
# gem install ssh_scan
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Use docker container to run, as follows:

# docker pull mozilla/ssh_scan
# docker run -it mozilla/ssh_scan /app/bin/ssh_scan -t github.com
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Use the source code to install and run, as follows:

# 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
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How to use ssh_scan on Linux

The syntax for using ssh_scan is as follows:

$ ssh_scan -t ip地址
$ ssh_scan -t 主机名
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For example, to scan the SSH configuration and policy of this server 192.168.43.198, type:

$ ssh_scan -t 192.168.43.198
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Note that you can also pass an [IP address/address range/host name] to the -t option as shown below:

$ ssh_scan -t 192.168.43.198,200,205
$ ssh_scan -t test.tecmint.lan
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Output example:

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]",
      "[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"
      ]
    }
  }
]
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You can use the -p option to specify different ports, the -L option to enable logging, and the -V option to specify the log level:

$ ssh_scan -t 192.168.43.198 -p 22222 -L ssh-scan.log -V INFO
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In addition, you can use the -P or --policy option to specify a policy file (the default is Mozilla Modern):

$ ssh_scan -t 192.168.43.198 -L ssh-scan.log -V INFO -P /path/to/custom/policy/file
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ssh_scan usage help and other examples:

$ ssh_scan -h
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Output example:

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
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SSH server related reference reading:

  1. Use SSH Keygen (ssh-keygen) in five steps to implement SSH password-free login
  2. 5 Best Practices for a Secure SSH Server
  3. Use Chroot to restrict SSH users from entering certain directories
  4. How to configure an SSH connection to simplify remote login

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source:linuxprobe.com
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