Link: Case-striped affiliate tracking token

 1name: "Link: Case-striped affiliate tracking token"
 2description: "Detects links carrying a known affiliate tracking token pattern. Observed in free kit, gift card, health and account suspension spam."
 3type: "rule"
 4severity: "medium"
 5source: |
 6  type.inbound
 7  and any(body.links,
 8          // link type digit (4 = click, 5 = unsubscribe), then digit fields split by fixed-length letter filler
 9          regex.contains(.href_url.url,
10                         '\b[45][A-Za-z]{5}\d+[A-Za-z]{4}\d+[a-z]{10}\d+[A-Z]{15}\d+[A-Z/]{1,4}\d+[A-Za-z]\d+\b'
11          )
12  )  
13attack_types:
14  - "Spam"
15tactics_and_techniques:
16  - "Free file host"
17  - "Punycode"
18  - "Evasion"
19detection_methods:
20  - "URL analysis"
21id: "940836a5-288c-57a0-9521-5dd612014299"