ssh-weak-public-key: SSH Host Keys < 2048 Bits Considered Weak

id: ssh-weak-public-key

info:
  name: SSH Host Keys < 2048 Bits Considered Weak
  author: pussycat0x
  severity: low
  description: |
    SSH host keys with a bit length below 2048 are deemed weak, posing an increased vulnerability to security threats. Employing robust key lengths is crucial for fortifying the integrity of encrypted communication and thwarting potential exploits.
  reference:
    - https://www.tenable.com/plugins/nessus/153954
  metadata:
    verified: true
    max-request: 2
    shodan-query: product:"OpenSSH"
  tags: enum,js,ssh,misconfig,network,vuln

variables:
  ecdsa_bit: '256' # 256 bytes = 2048 bits
  rsa_bit: '2048' # 2048 bits

javascript:
  - pre-condition: |
      isPortOpen(Host,Port);
    code: |
      let m = require("nuclei/ssh");
      let c = m.SSHClient();
      let response = c.ConnectSSHInfoMode(Host, Port);
      Export(response);
    args:
      Host: "{{Host}}"
      Port: "22"

    matchers-condition: and
    matchers:
      - type: word
        words:
          - "server_host_key"

      - type: dsl
        dsl:
          - 'len(ecdsa_keylen) != 0 && ecdsa_keylen < ecdsa_bit'
          - 'len(rsa_keylen) !=0 && rsa_keylen < rsa_bit'

    extractors:
      - type: json
        internal: true
        name: ecdsa_keylen
        json:
          - '.DHKeyExchange.server_host_key.ecdsa_public_key.length'

      - type: json
        internal: true
        name: rsa_keylen
        json:
          - '.DHKeyExchange.server_host_key.rsa_public_key.length'
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