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Detection rules › Sublime MQL

File sharing link from suspicious sender domain

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

A file sharing link in the body sent from a suspicious sender domain.

Threat classification

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

CategoryValues
Attack typesCredential Phishing, Malware/Ransomware
Tactics and techniquesFree file host

Event coverage

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

Rule body MQL

type.inbound
and any(body.links,
        (
          .href_url.domain.domain in $free_file_hosts
          or .href_url.domain.root_domain in $free_file_hosts
        )
        and not .href_url.domain.domain in $tenant_domains
        // remove free_file_hosts used to host images as links
        and not any($file_types_images,
                    strings.iends_with(..href_url.url, strings.concat('.', .))
        )
)
and sender.email.domain.tld in $suspicious_tlds
and not sender.email.domain.root_domain in ("notion.so", "cribl.cloud")
and (
  not profile.by_sender().solicited
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)

Detection logic

Scope: inbound message.

A file sharing link in the body sent from a suspicious sender domain.

  1. inbound message
  2. any of body.links where all hold:
    • any of:
      • .href_url.domain.domain in $free_file_hosts
      • .href_url.domain.root_domain in $free_file_hosts
    • not:
      • .href_url.domain.domain in $tenant_domains
    • not:
      • any of $file_types_images where:
        • strings.iends_with(.href_url.url)
  3. sender.email.domain.tld in $suspicious_tlds
  4. not:
    • sender.email.domain.root_domain in ('notion.so', 'cribl.cloud')
  5. any of:
    • not:
      • profile.by_sender().solicited
    • 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.domain, body.links[].href_url.domain.root_domain, body.links[].href_url.url, sender.email.domain.root_domain, sender.email.domain.tld, type.inbound. Sensors: profile.by_sender, strings.concat, strings.iends_with. Reference lists: $file_types_images, $free_file_hosts, $suspicious_tlds, $tenant_domains.

Indicators matched (2)

FieldMatchValue
sender.email.domain.root_domainmembernotion.so
sender.email.domain.root_domainmembercribl.cloud