Credential phishing: 'Secure message' and engaging language

  1name: "Credential phishing: 'Secure message' and engaging language"
  2description: |
  3    Body contains language resembling credential theft, and a "secure message" from an untrusted sender.
  4type: "rule"
  5severity: "medium"
  6source: |
  7  type.inbound
  8  and (
  9    (
 10      any(ml.nlu_classifier(body.current_thread.text).intents,
 11          .name == "cred_theft" and .confidence == "high"
 12      )
 13      or any(body.current_thread.links,
 14             regex.icontains(.display_text, '(?:read|view|open) the message')
 15             and (
 16               .href_url.domain.root_domain not in $tranco_1m
 17               or .href_url.domain.domain in $free_file_hosts
 18               or .href_url.domain.root_domain in $free_file_hosts
 19               or .href_url.domain.root_domain in $free_subdomain_hosts
 20               or .href_url.domain.domain in $url_shorteners
 21               or .href_url.domain.domain in $social_landing_hosts
 22             )
 23      )
 24    )
 25    or any(ml.nlu_classifier(beta.ocr(file.message_screenshot()).text).intents,
 26           .name == "cred_theft" and .confidence in ("medium", "high")
 27    )
 28  )
 29  and (
 30    (
 31      regex.icontains(body.current_thread.text,
 32                      "secured? (message|directory|document|file)"
 33      )
 34      or regex.icontains(subject.base,
 35                         "secured? (message|directory|document|file)"
 36      )
 37      or strings.icontains(body.current_thread.text, "document portal")
 38      or strings.icontains(body.current_thread.text, "encrypted message")
 39      or strings.icontains(body.current_thread.text, "protected message")
 40    )
 41    or any(body.previous_threads,
 42           regex.icontains(.text, "secured? (message|directory|document|file)")
 43           or strings.icontains(.text, "document portal")
 44           or strings.icontains(.text, "encrypted message")
 45           or strings.icontains(.text, "protected message")
 46    )
 47    or any(body.current_thread.links,
 48           regex.icontains(ml.link_analysis(.).final_dom.display_text,
 49                           'secured? (?:message|directory|document|file) access'
 50           )
 51           or regex.icontains(ml.link_analysis(.).final_dom.inner_text,
 52                              'secured? (?:message|directory|document|file) access'
 53           )
 54    )
 55    or (
 56      length(filter(ml.nlu_classifier(body.current_thread.text).entities,
 57                    .name == "urgency"
 58             )
 59      ) >= 2
 60      and any(ml.nlu_classifier(body.current_thread.text).topics,
 61              .name == "Secure Message" and .confidence != "low"
 62      )
 63    )
 64  )
 65  // has at least 1 link
 66  and length(body.links) > 0
 67  
 68  // negate legitimate message senders
 69  and (
 70    sender.email.domain.root_domain not in ("protectedtrust.com")
 71    and any(body.links,
 72            .href_url.domain.root_domain != sender.email.domain.root_domain
 73    )
 74    // negate known secure mailers
 75    and not all(body.links,
 76                .href_url.domain.root_domain in (
 77                  "mimecast.com",
 78                  "cisco.com",
 79                  "csiesafe.com"
 80                )
 81    )
 82    and any(headers.hops,
 83            .index == 0
 84            and not any(.fields,
 85                        strings.contains(.value,
 86                                         'multipart/mixed; boundary="PROOFPOINT_BOUNDARY_1"'
 87                        )
 88            )
 89    )
 90    and not (
 91      length(filter(attachments,
 92                    strings.ilike(.file_name,
 93                                  "logo.*",
 94                                  "lock.gif",
 95                                  "SecureMessageAtt.html"
 96                    )
 97             )
 98      ) == 3
 99      and any(attachments,
100              .file_type == "html"
101              and any(file.explode(.),
102                      .scan.html.title == "Proofpoint Encryption"
103                      and any(.scan.url.urls,
104                              strings.iends_with(.path,
105                                                 'formpostdir/safeformpost.aspx'
106                              )
107                      )
108              )
109              and strings.count(file.parse_html(.).raw, 'name="msg') > 3
110      )
111    )
112    and not (
113      any(headers.hops,
114          any(.fields,
115              .name in (
116                'X-ZixNet',
117                'X-VPM-MIV',
118                'X-VPM-ActionCode',
119                'X-VPM-SmtpTo'
120              )
121          )
122      )
123      and any(headers.domains,
124              .root_domain in (
125                "zixport.com",
126                "zixcorp.com",
127                "zixmail.net",
128                "zixworks.com"
129              )
130      )
131    )
132    and not (
133      any(headers.hops, any(.fields, .name == 'X-SendInc-Message-Id'))
134      and any(headers.domains, .root_domain in ("sendinc.net"))
135    )
136    // negating Mimecast sends with MS banner and/or sender's email pulled out as a link
137    and not length(filter(body.links,
138                          (
139                            .display_text is null
140                            and .display_url.url == sender.email.domain.root_domain
141                          )
142                          or .href_url.domain.root_domain in (
143                            "aka.ms",
144                            "mimecast.com",
145                            "cisco.com"
146                          )
147                   )
148    ) == length(body.links)
149  )
150  and (
151    (
152      profile.by_sender().prevalence in ("new", "outlier")
153      and not profile.by_sender().solicited
154    )
155    or (
156      profile.by_sender().any_messages_malicious_or_spam
157      and not profile.by_sender().any_messages_benign
158    )
159    // or the sender is all undisclosed or there are no recipients
160    or (
161      length(recipients.to) == 0
162      or all(recipients.to,
163             strings.ilike(.display_name, "undisclosed?recipients")
164      )
165    )
166    // or the sender exhibits a "self sender" pattern
167    or (
168      length(recipients.to) == 1
169      and any(recipients.to, .email.email == sender.email.email)
170    )
171  )
172  and not profile.by_sender().any_messages_benign
173  and not (
174    sender.email.domain.root_domain in $high_trust_sender_root_domains
175    and coalesce(headers.auth_summary.dmarc.pass, false)
176  )  
177attack_types:
178  - "Credential Phishing"
179tactics_and_techniques:
180  - "Social engineering"
181detection_methods:
182  - "Natural Language Understanding"
183  - "Sender analysis"
184id: "bd95a7b1-dc96-53c1-bb7c-3a0f98b04744"