detection.wiki

Detection rules › Sublime MQL

Spam: New link domain (<=10d) and emojis

Severity
medium
Type
rule
Source
github.com/sublime-security/sublime-rules

Detects spam from freemail senders, where the linked domain is less than 10 days old and emojis present.

Threat classification

Sublime's own taxonomy (not MITRE ATT&CK).

CategoryValues
Attack typesSpam
Tactics and techniquesFree email provider

Event coverage

Message attribute
body
body.links (collection)
body.plain
sender.email
subject
type

Rule body MQL

type.inbound

// sender is a freemail
and sender.email.domain.root_domain in $free_email_providers

// linked domain is less than 10 days old
and any(body.links, network.whois(.href_url.domain).days_old < 10)

// has an emoji in the subject or body
and (
  regex.contains(body.plain.raw,
                 '[\x{1F300}-\x{1F5FF}\x{1F600}-\x{1F64F}\x{1F680}-\x{1F6FF}\x{1F700}-\x{1F77F}\x{1F780}-\x{1F7FF}\x{1F900}-\x{1F9FF}\x{2600}-\x{26FF}\x{2700}-\x{27BF}\x{2300}-\x{23FF}]'
  )
  or regex.contains(subject.subject,
                    '[\x{1F300}-\x{1F5FF}\x{1F600}-\x{1F64F}\x{1F680}-\x{1F6FF}\x{1F700}-\x{1F77F}\x{1F780}-\x{1F7FF}\x{1F900}-\x{1F9FF}\x{2600}-\x{26FF}\x{2700}-\x{27BF}\x{2300}-\x{23FF}]'
  )
)
and (
  profile.by_sender().prevalence in ("new", "outlier")
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)

Detection logic

Scope: inbound message.

Detects spam from freemail senders, where the linked domain is less than 10 days old and emojis present.

  1. inbound message
  2. sender.email.domain.root_domain in $free_email_providers
  3. any of body.links where:
    • network.whois(.href_url.domain).days_old < 10
  4. any of:
    • body.plain.raw matches '[\\x{1F300}-\\x{1F5FF}\\x{1F600}-\\x{1F64F}\\x{1F680}-\\x{1F6FF}\\x{1F700}-\\x{1F77F}\\x{1F780}-\\x{1F7FF}\\x{1F900}-\\x{1F9FF}\\x{2600}-\\x{26FF}\\x{2700}-\\x{27BF}\\x{2300}-\\x{23FF}]'
    • subject.subject matches '[\\x{1F300}-\\x{1F5FF}\\x{1F600}-\\x{1F64F}\\x{1F680}-\\x{1F6FF}\\x{1F700}-\\x{1F77F}\\x{1F780}-\\x{1F7FF}\\x{1F900}-\\x{1F9FF}\\x{2600}-\\x{26FF}\\x{2700}-\\x{27BF}\\x{2300}-\\x{23FF}]'
  5. any of:
    • profile.by_sender().prevalence in ('new', 'outlier')
    • all of:
      • profile.by_sender().any_messages_malicious_or_spam
      • not:
        • profile.by_sender().any_messages_benign

Inspects: body.links, body.links[].href_url.domain, body.plain.raw, sender.email.domain.root_domain, subject.subject, type.inbound. Sensors: network.whois, profile.by_sender, regex.contains. Reference lists: $free_email_providers.

Indicators matched (1)

FieldMatchValue
regex.containsregex[\x{1F300}-\x{1F5FF}\x{1F600}-\x{1F64F}\x{1F680}-\x{1F6FF}\x{1F700}-\x{1F77F}\x{1F780}-\x{1F7FF}\x{1F900}-\x{1F9FF}\x{2600}-\x{26FF}\x{2700}-\x{27BF}\x{2300}-\x{23FF}]