Detection rules › Sublime MQL
File sharing link with a suspicious subject
A file sharing link in the body with a common BEC subject. This rule could be expanded to include additional BEC subjects.
Threat classification
Sublime's own taxonomy (not MITRE ATT&CK).
| Category | Values |
|---|---|
| Attack types | BEC/Fraud |
| Tactics and techniques | Free file host, Social engineering |
Event coverage
Rule body MQL
type.inbound
and sender.email.domain.root_domain != 'google.com'
and not (
sender.email.domain.root_domain == "dropbox.com"
and headers.auth_summary.dmarc.pass
)
and any(body.links,
(
.href_url.domain.domain in $free_file_hosts
or .href_url.domain.root_domain in $free_file_hosts
)
and not (
// negating Google Forms links
.href_url.domain.domain == "docs.google.com"
and strings.istarts_with(.href_url.path, "/forms/")
)
and not .href_url.domain.domain in $tenant_domains
)
and regex.icontains(subject.subject, 'immediately', 'urgent')
and any(ml.nlu_classifier(body.current_thread.text).intents, .name != "benign")
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 with a common BEC subject. This rule could be expanded to include additional BEC subjects.
- inbound message
- sender.email.domain.root_domain is not 'google.com'
not:
all of:
- sender.email.domain.root_domain is 'dropbox.com'
- headers.auth_summary.dmarc.pass
any of
body.linkswhere all hold:any of:
- .href_url.domain.domain in $free_file_hosts
- .href_url.domain.root_domain in $free_file_hosts
not:
all of:
- .href_url.domain.domain is 'docs.google.com'
- .href_url.path starts with '/forms/'
not:
- .href_url.domain.domain in $tenant_domains
subject.subject matches any of 2 patterns
immediatelyurgent
any of
ml.nlu_classifier(body.current_thread.text).intentswhere:- .name is not 'benign'
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.current_thread.text, body.links, body.links[].href_url.domain.domain, body.links[].href_url.domain.root_domain, body.links[].href_url.path, headers.auth_summary.dmarc.pass, sender.email.domain.root_domain, subject.subject, type.inbound. Sensors: ml.nlu_classifier, profile.by_sender, regex.icontains, strings.istarts_with. Reference lists: $free_file_hosts, $tenant_domains.
Indicators matched (5)
| Field | Match | Value |
|---|---|---|
sender.email.domain.root_domain | equals | dropbox.com |
body.links[].href_url.domain.domain | equals | docs.google.com |
strings.istarts_with | prefix | /forms/ |
regex.icontains | regex | immediately |
regex.icontains | regex | urgent |