sublimemediumRule

Reconnaissance: Hotel booking reply-to redirect

Detects messages impersonating hotel booking inquiries by identifying common hotel-related language patterns from senders where the reply-to is a free email provider and differs from the sender domain in an effort to validate whether a recipient address is valid or not, potentially preceding an attack.

MITRE ATT&CK

T1566.002 T1534 T1656 T1566 T1598

initial-access

Detection Query

type.inbound
and any(headers.reply_to,
        .email.domain.root_domain in $free_email_providers
        and .email.domain.root_domain != sender.email.domain.root_domain
)
and all(recipients.to,
        .email.domain.root_domain != sender.email.domain.root_domain
)
and length(body.links) == 0
and length(attachments) == 0
and length(body.current_thread.text) < 600
and not (
  (subject.is_reply or subject.is_forward)
  and (length(headers.references) > 0 or headers.in_reply_to is not null)
)
and (
  (
    strings.ilike(body.current_thread.text,
                  '*hotel*',
                  '*your property*',
                  '*accommodation*',
                  '*guest services*',
                  '*reception*',
                  '*front desk*'
    )
    and strings.ilike(body.current_thread.text,
                      '*booking*',
                      '*to book*',
                      '*book a *',
                      '*reserv*',
                      '*room*',
                      '*suite*',
                      '*availability*',
                      '*check-in*',
                      '*available dates*',
                      '*family trip*',
                      '*deluxe accommodation*',
                      '*two children*',
                      '*hotel manager*'
    )
  )
  or strings.ilike(subject.base,
                   '*hotel*',
                   '*room reserv*',
                   '*room inquiry*',
                   '*room availability*',
                   '*suite*',
                   '*accommodation*'
  )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Reconnaissance: Hotel booking reply-to redirect"
description: "Detects messages impersonating hotel booking inquiries by identifying common hotel-related language patterns from senders where the reply-to is a free email provider and differs from the sender domain in an effort to validate whether a recipient address is valid or not, potentially preceding an attack."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(headers.reply_to,
          .email.domain.root_domain in $free_email_providers
          and .email.domain.root_domain != sender.email.domain.root_domain
  )
  and all(recipients.to,
          .email.domain.root_domain != sender.email.domain.root_domain
  )
  and length(body.links) == 0
  and length(attachments) == 0
  and length(body.current_thread.text) < 600
  and not (
    (subject.is_reply or subject.is_forward)
    and (length(headers.references) > 0 or headers.in_reply_to is not null)
  )
  and (
    (
      strings.ilike(body.current_thread.text,
                    '*hotel*',
                    '*your property*',
                    '*accommodation*',
                    '*guest services*',
                    '*reception*',
                    '*front desk*'
      )
      and strings.ilike(body.current_thread.text,
                        '*booking*',
                        '*to book*',
                        '*book a *',
                        '*reserv*',
                        '*room*',
                        '*suite*',
                        '*availability*',
                        '*check-in*',
                        '*available dates*',
                        '*family trip*',
                        '*deluxe accommodation*',
                        '*two children*',
                        '*hotel manager*'
      )
    )
    or strings.ilike(subject.base,
                     '*hotel*',
                     '*room reserv*',
                     '*room inquiry*',
                     '*room availability*',
                     '*suite*',
                     '*accommodation*'
    )
  )
attack_types:
  - "BEC/Fraud"
tactics_and_techniques:
  - "Free email provider"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Sender analysis"
id: "08c36035-dc50-5169-808c-c8a6d2f64932"