Detection rules › Sublime MQL
Attachment: DocuSign impersonation via PDF linking to new domain
This rule detects PDF files containing a DocuSign logo linking to a newly created domain (Less than or equal to 3 days)
Threat classification
Sublime's own taxonomy (not MITRE ATT&CK).
| Category | Values |
|---|---|
| Attack types | Credential Phishing |
| Tactics and techniques | Impersonation: Brand, PDF, Social engineering |
Event coverage
Rule body MQL
type.inbound
and any(attachments,
.file_type == "pdf"
and any(ml.logo_detect(.).brands, .name == "DocuSign")
and any(file.explode(.),
any(.scan.pdf.urls, network.whois(.domain).days_old <= 3)
)
)
// negate highly trusted sender domains unless they fail DMARC authentication
and (
(
sender.email.domain.root_domain in $high_trust_sender_root_domains
and not headers.auth_summary.dmarc.pass
)
or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)
// excludes senders that contain "via" in the display name a resilient way
and not (
any(headers.hops,
any(.fields,
.name == "X-Api-Host" and strings.ends_with(.value, "docusign.net")
)
)
)
Detection logic
Scope: inbound message.
This rule detects PDF files containing a DocuSign logo linking to a newly created domain (Less than or equal to 3 days)
- inbound message
any of
attachmentswhere all hold:- .file_type is 'pdf'
any of
ml.logo_detect(.).brandswhere:- .name is 'DocuSign'
any of
file.explode(.)where:any of
.scan.pdf.urlswhere:- network.whois(.domain).days_old ≤ 3
any of:
all of:
- sender.email.domain.root_domain in $high_trust_sender_root_domains
not:
- headers.auth_summary.dmarc.pass
- sender.email.domain.root_domain not in $high_trust_sender_root_domains
not:
any of
headers.hopswhere:any of
.fieldswhere all hold:- .name is 'X-Api-Host'
- .value ends with 'docusign.net'
Inspects: attachments[].file_type, headers.auth_summary.dmarc.pass, headers.hops, headers.hops[].fields, headers.hops[].fields[].name, headers.hops[].fields[].value, sender.email.domain.root_domain, type.inbound. Sensors: file.explode, ml.logo_detect, network.whois, strings.ends_with. Reference lists: $high_trust_sender_root_domains.
Indicators matched (4)
| Field | Match | Value |
|---|---|---|
attachments[].file_type | equals | pdf |
ml.logo_detect(attachments[]).brands[].name | equals | DocuSign |
headers.hops[].fields[].name | equals | X-Api-Host |
strings.ends_with | suffix | docusign.net |