Detection rules › Sublime MQL
Attachment: Callback phishing solicitation via text-based file
Callback Phishing via a text-based file attachment and a short body and subject from an unknown sender.
Threat classification
Sublime's own taxonomy (not MITRE ATT&CK).
| Category | Values |
|---|---|
| Attack types | Callback Phishing |
| Tactics and techniques | Evasion, Out of band pivot, Social engineering |
Event coverage
Rule body MQL
type.inbound
and length(subject.subject) <= 10
// there are no links, all the links are to aka.ms, or an extraction from a warning banner that match the senders domain
and (
length(body.links) == 0
or length(filter(body.links,
(
.display_text is null
and .display_url.url == sender.email.domain.root_domain
)
or .href_url.domain.domain == "aka.ms"
or network.whois(.display_url.domain).days_old < 30
)
) == length(body.links)
)
and (body.current_thread.text is null or length(body.current_thread.text) < 50)
and 0 < length(attachments) < 4
and any(attachments,
(
.content_type == "text/plain"
or .file_type in ("doc", "docx", "xls", "xlsx")
)
and any(file.explode(.),
(.depth == 0 or .flavors.mime == "text/plain")
// 4 of the following strings are found
and 4 of (
// this section is synced with attachment_callback_phish_with_pdf.yml and body_callback_phishing_no_attachment.yml
strings.icontains(.scan.strings.raw, "purchase"),
strings.icontains(.scan.strings.raw, "payment"),
strings.icontains(.scan.strings.raw, "transaction"),
strings.icontains(.scan.strings.raw, "subscription"),
strings.icontains(.scan.strings.raw, "antivirus"),
strings.icontains(.scan.strings.raw, "order"),
strings.icontains(.scan.strings.raw, "support"),
strings.icontains(.scan.strings.raw, "help line"),
strings.icontains(.scan.strings.raw, "receipt"),
strings.icontains(.scan.strings.raw, "invoice"),
strings.icontains(.scan.strings.raw, "call"),
strings.icontains(.scan.strings.raw, "helpdesk"),
strings.icontains(.scan.strings.raw, "cancel"),
strings.icontains(.scan.strings.raw, "renew"),
strings.icontains(.scan.strings.raw, "refund"),
regex.icontains(.scan.strings.raw, "(?:reach|contact) us at"),
strings.icontains(.scan.strings.raw, "+1"),
strings.icontains(.scan.strings.raw, "amount"),
strings.icontains(.scan.strings.raw, "charged"),
strings.icontains(.scan.strings.raw, "crypto"),
strings.icontains(.scan.strings.raw, "wallet address"),
regex.icontains(.scan.strings.raw, '\$\d{3}\.\d{2}\b'),
regex.icontains(.scan.strings.raw,
'\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}',
'\+?([ilo0-9]{1,2})?\s?\(?\d{3}\)?[\s\.\-⋅]{0,5}[ilo0-9]{3}[\s\.\-⋅]{0,5}[ilo0-9]{4}'
),
)
// this section is synced with attachment_callback_phish_with_pdf.yml and body_callback_phishing_no_attachment.yml
and regex.icontains(.scan.strings.raw,
'(p.{0,3}a.{0,3}y.{0,3}p.{0,3}a.{0,3}l|ma?c.?fee|n[o0]rt[o0]n|geek.{0,5}squad|ebay|symantec|best buy|lifel[o0]c|secure anywhere|starz|utilities premium|pc security|at&t)'
)
)
)
and profile.by_sender().prevalence != "common"
and not profile.by_sender().solicited
and not profile.by_sender().any_messages_benign
// negate highly trusted sender domains unless they fail DMARC authentication
and (
(
sender.email.domain.root_domain in $high_trust_sender_root_domains
and (
any(distinct(headers.hops, .authentication_results.dmarc is not null),
strings.ilike(.authentication_results.dmarc, "*fail")
)
)
)
or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)
Detection logic
Scope: inbound message.
Callback Phishing via a text-based file attachment and a short body and subject from an unknown sender.
- inbound message
- length(subject.subject) ≤ 10
any of:
- length(body.links) is 0
- length(filter(body.links, .display_text is null and .display_url.url == sender.email.domain.root_domain or .href_url.domain.domain == 'aka.ms' or network.whois(.display_url.domain).days_old < 30)) is length(body.links)
any of:
- body.current_thread.text is missing
- length(body.current_thread.text) < 50
all of:
- length(attachments) > 0
- length(attachments) < 4
any of
attachmentswhere all hold:any of:
- .content_type is 'text/plain'
- .file_type in ('doc', 'docx', 'xls', 'xlsx')
any of
file.explode(.)where all hold:any of:
- .depth is 0
- .flavors.mime is 'text/plain'
at least 4 of:
- .scan.strings.raw contains 'purchase'
- .scan.strings.raw contains 'payment'
- .scan.strings.raw contains 'transaction'
- .scan.strings.raw contains 'subscription'
- .scan.strings.raw contains 'antivirus'
- .scan.strings.raw contains 'order'
- .scan.strings.raw contains 'support'
- .scan.strings.raw contains 'help line'
- .scan.strings.raw contains 'receipt'
- .scan.strings.raw contains 'invoice'
- .scan.strings.raw contains 'call'
- .scan.strings.raw contains 'helpdesk'
- .scan.strings.raw contains 'cancel'
- .scan.strings.raw contains 'renew'
- .scan.strings.raw contains 'refund'
- .scan.strings.raw matches '(?:reach|contact) us at'
- .scan.strings.raw contains '+1'
- .scan.strings.raw contains 'amount'
- .scan.strings.raw contains 'charged'
- .scan.strings.raw contains 'crypto'
- .scan.strings.raw contains 'wallet address'
- .scan.strings.raw matches '\\$\\d{3}\\.\\d{2}\\b'
.scan.strings.raw matches any of 2 patterns
\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}\+?([ilo0-9]{1,2})?\s?\(?\d{3}\)?[\s\.\-⋅]{0,5}[ilo0-9]{3}[\s\.\-⋅]{0,5}[ilo0-9]{4}
- .scan.strings.raw matches '(p.{0,3}a.{0,3}y.{0,3}p.{0,3}a.{0,3}l|ma?c.?fee|n[o0]rt[o0]n|geek.{0,5}squad|ebay|symantec|best buy|lifel[o0]c|secure anywhere|starz|utilities premium|pc security|at&t)'
- profile.by_sender().prevalence is not 'common'
not:
- profile.by_sender().solicited
not:
- profile.by_sender().any_messages_benign
any of:
all of:
- sender.email.domain.root_domain in $high_trust_sender_root_domains
any of
distinct(headers.hops)where:- .authentication_results.dmarc matches '*fail'
- sender.email.domain.root_domain not in $high_trust_sender_root_domains
Inspects: attachments[].content_type, attachments[].file_type, body.current_thread.text, body.links, body.links[].display_text, body.links[].display_url.domain, body.links[].display_url.url, body.links[].href_url.domain.domain, headers.hops, headers.hops[].authentication_results.dmarc, sender.email.domain.root_domain, subject.subject, type.inbound. Sensors: file.explode, network.whois, profile.by_sender, regex.icontains, strings.icontains, strings.ilike. Reference lists: $high_trust_sender_root_domains.
Indicators matched (33)
| Field | Match | Value |
|---|---|---|
body.links[].href_url.domain.domain | equals | aka.ms |
attachments[].content_type | equals | text/plain |
attachments[].file_type | member | doc |
attachments[].file_type | member | docx |
attachments[].file_type | member | xls |
attachments[].file_type | member | xlsx |
file.explode(attachments[])[].flavors.mime | equals | text/plain |
strings.icontains | substring | purchase |
strings.icontains | substring | payment |
strings.icontains | substring | transaction |
strings.icontains | substring | subscription |
strings.icontains | substring | antivirus |
21 more
strings.icontains | substring | order |
strings.icontains | substring | support |
strings.icontains | substring | help line |
strings.icontains | substring | receipt |
strings.icontains | substring | invoice |
strings.icontains | substring | call |
strings.icontains | substring | helpdesk |
strings.icontains | substring | cancel |
strings.icontains | substring | renew |
strings.icontains | substring | refund |
regex.icontains | regex | (?:reach|contact) us at |
strings.icontains | substring | +1 |
strings.icontains | substring | amount |
strings.icontains | substring | charged |
strings.icontains | substring | crypto |
strings.icontains | substring | wallet address |
regex.icontains | regex | \$\d{3}\.\d{2}\b |
regex.icontains | regex | \+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4} |
regex.icontains | regex | \+?([ilo0-9]{1,2})?\s?\(?\d{3}\)?[\s\.\-⋅]{0,5}[ilo0-9]{3}[\s\.\-⋅]{0,5}[ilo0-9]{4} |
regex.icontains | regex | (p.{0,3}a.{0,3}y.{0,3}p.{0,3}a.{0,3}l|ma?c.?fee|n[o0]rt[o0]n|geek.{0,5}squad|ebay|symantec|best buy|lifel[o0]c|secure anywhere|starz|utilities premium|pc security|at&t) |
strings.ilike | substring | *fail |