id: expn-mail-detect

info:
  name: EXPN Mail Server Detect
  author: r3dg33k
  severity: info
  description: |
    The "EXPN" can be used by attackers to learn about valid usernames on the target system. On some SMTP servers, EXPN can be used to show the subscribers of a mailing list subscription lists are generally considered to be sensitive information.
  tags: mail,expn,network,detect
  metadata:
    max-request: 2

tcp:
  - inputs:
      - data: "65686c6f20636865636b746c730a"
        type: hex
    read-size: 2048

    host:
      - "{{Hostname}}"
      - "{{Host}}:25"

    matchers:
      - type: word
        words:
          - "250-EXPN"