Detection rules › Sublime MQL

Sublime MQL rules: urlhaus

Rule	Severity
URLhaus: Malicious domain in message body or pdf attachment (trusted reporters)	`medium`

URLhaus: Malicious domain in message body or pdf attachment (trusted reporters)

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

Detects URLhaus domains submitted by trusted reporters in message bodies or pdf attachments

Threat classification

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

Category	Values
Attack types	Credential Phishing, Malware/Ransomware
Tactics and techniques	PDF

Telemetry coverage

Platform	Record / event type
Sublime	Inbound email message

Message attributes

attachments
body
body.links
type

Rule body

type.inbound
and (
  any(body.links,
      // filter potentially known good domains
      // prevents FPs on entries such as drive[.]google[.]com, or
      // other accidental pushes to the List
      .href_url.domain.domain not in $free_file_hosts
      and .href_url.domain.root_domain not in $free_file_hosts
      and .href_url.domain.domain not in $tranco_1m
      and .href_url.domain.domain not in $umbrella_1m

      // this ensures we don't flag on legit FQDNs that
      // aren't in the Tranco 1M, but their root domains are
      // eg: support[.]google[.]com
      and .href_url.domain.root_domain not in $tranco_1m
      and .href_url.domain.root_domain not in $umbrella_1m
      and .href_url.domain.root_domain not in $free_subdomain_hosts
      and .href_url.domain.root_domain in $abuse_ch_urlhaus_domains_trusted_reporters
  )
  or any(attachments,
         .file_type == "pdf"
         and any(file.explode(.),
                 any(.scan.pdf.urls,
                     // filter potentially known good domains
                     // prevents FPs on entries such as drive[.]google[.]com, or
                     // other accidental pushes to the List
                     .domain.domain not in $free_file_hosts
                     and .domain.root_domain not in $free_file_hosts
                     and .domain.domain not in $free_subdomain_hosts
                     and .domain.domain not in $tranco_1m
                     and .domain.domain not in $umbrella_1m

                     // this ensures we don't flag on legit FQDNs that
                     // aren't in the Tranco 1M, but their root domains are
                     // eg: support[.]google[.]com
                     and .domain.root_domain not in $tranco_1m
                     and .domain.root_domain not in $umbrella_1m
                     and .domain.domain in $abuse_ch_urlhaus_domains_trusted_reporters
                 )
         )
  )
)

Detection logic

Scope: inbound message.

Detects URLhaus domains submitted by trusted reporters in message bodies or pdf attachments

inbound message
any of:
- any of body.links where all hold:
  - .href_url.domain.domain not in $free_file_hosts
  - .href_url.domain.root_domain not in $free_file_hosts
  - .href_url.domain.domain not in $tranco_1m
  - .href_url.domain.domain not in $umbrella_1m
  - .href_url.domain.root_domain not in $tranco_1m
  - .href_url.domain.root_domain not in $umbrella_1m
  - .href_url.domain.root_domain not in $free_subdomain_hosts
  - .href_url.domain.root_domain in $abuse_ch_urlhaus_domains_trusted_reporters
- any of attachments where all hold:
  - .file_type is 'pdf'
  - any of file.explode(.) where:
    
    any of .scan.pdf.urls where all hold:
    
    .domain.domain not in $free_file_hosts
    .domain.root_domain not in $free_file_hosts
    .domain.domain not in $free_subdomain_hosts
    .domain.domain not in $tranco_1m
    .domain.domain not in $umbrella_1m
    .domain.root_domain not in $tranco_1m
    .domain.root_domain not in $umbrella_1m
    .domain.domain in $abuse_ch_urlhaus_domains_trusted_reporters

Inspects: attachments[].file_type, body.links, body.links[].href_url.domain.domain, body.links[].href_url.domain.root_domain, type.inbound. Sensors: file.explode. Reference lists: $abuse_ch_urlhaus_domains_trusted_reporters, $free_file_hosts, $free_subdomain_hosts, $tranco_1m, $umbrella_1m.

Indicators matched (1)

Field	Match	Value
`attachments[].file_type`	equals	`pdf`

Stages and Predicates

Stage 1: `mql_rule`

and
  or
    any(attachments)
      and
        any(file.explode(attachments))
          any(file.explode(attachments).scan.pdf.urls)
            and
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.domain in abuse_ch_urlhaus_domains_trusted_reporters"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.domain not in free_file_hosts"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.domain not in free_subdomain_hosts"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.domain not in tranco_1m"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.domain not in umbrella_1m"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.root_domain not in free_file_hosts"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.root_domain not in tranco_1m"
               macro "file.explode(attachments[])[].scan.pdf.urls[].domain.root_domain not in umbrella_1m"
        attachments.file_type eq "pdf"
    any(body.links)
      and
         macro "body.links[].href_url.domain.domain not in free_file_hosts"
         macro "body.links[].href_url.domain.domain not in tranco_1m"
         macro "body.links[].href_url.domain.domain not in umbrella_1m"
         macro "body.links[].href_url.domain.root_domain in abuse_ch_urlhaus_domains_trusted_reporters"
         macro "body.links[].href_url.domain.root_domain not in free_file_hosts"
         macro "body.links[].href_url.domain.root_domain not in free_subdomain_hosts"
         macro "body.links[].href_url.domain.root_domain not in tranco_1m"
         macro "body.links[].href_url.domain.root_domain not in umbrella_1m"
  type.inbound eq "true"

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`type.inbound`	eq	`true` transforms: `boolean`	`field:"type.inbound" kind:eq value:"true"`