Constant Contact link infrastructure abuse

  1name: "Constant Contact link infrastructure abuse"
  2description: "Email contains a Constant Contact (mass mailing platform) tracking link but does not originate from Constant Contact sending infrastructure. The rs6.net domain has been abused by threat actors to attempt credential phishing."
  3type: "rule"
  4severity: "high"
  5source: |
  6  type.inbound
  7  and (
  8    (
  9      length(body.links) < 15
 10      and any(body.links,
 11              .href_url.domain.root_domain in (
 12                "rs6.net",
 13                "constantcontactpages.com"
 14              )
 15      )
 16    )
 17    or (
 18      length(attachments) <= 3
 19      and (
 20        any(attachments,
 21            (.file_type in $file_types_images or .file_type == "pdf")
 22            //
 23            // This rule makes use of a beta feature and is subject to change without notice
 24            // using the beta feature in custom rules is not suggested until it has been formally released
 25            //
 26            and any(beta.scan_qr(.).items,
 27                    .type is not null
 28                    and .url.domain.root_domain in (
 29                      "rs6.net",
 30                      "constantcontactpages.com"
 31                    )
 32            )
 33            //
 34            // This rule makes use of a beta feature and is subject to change without notice
 35            // using the beta feature in custom rules is not suggested until it has been formally released
 36            //
 37            // exclude images taken with mobile cameras and screenshots from android
 38            and not any(beta.parse_exif(.).fields,
 39                        .key == "Model"
 40                        or (
 41                          .key == "Software"
 42                          and strings.starts_with(.value, "Android")
 43                        )
 44            )
 45            // exclude images taken with mobile cameras and screenshots from Apple
 46            and not any(beta.parse_exif(.).fields,
 47                        .key == "DeviceManufacturer"
 48                        and .value == "Apple Computer Inc."
 49            )
 50        )
 51        or (
 52          length(attachments) == 0
 53          and (
 54            //
 55            // This rule makes use of a beta feature and is subject to change without notice
 56            // using the beta feature in custom rules is not suggested until it has been formally released
 57            //
 58            beta.parse_exif(file.message_screenshot()).image_height < 2000
 59            and beta.parse_exif(file.message_screenshot()).image_width < 2000
 60            and beta.scan_qr(file.message_screenshot()).found
 61            and any(beta.scan_qr(file.message_screenshot()).items,
 62                    .type is not null and .url.domain.root_domain == "rs6.net"
 63            )
 64          )
 65        )
 66      )
 67    )
 68  )
 69  and not (
 70    any(headers.hops,
 71        strings.icontains(.authentication_results.spf_details.designator,
 72                          "constantcontact.com"
 73        )
 74    )
 75    or any(headers.hops,
 76           strings.icontains(.received_spf.designator, "constantcontact.com")
 77    )
 78    or (
 79      (
 80        any(headers.hops,
 81            any(.authentication_results.dkim_details,
 82                .domain == "auth.ccsend.com"
 83            )
 84        )
 85      )
 86      and headers.auth_summary.dmarc.pass
 87    )
 88    or any(headers.references, strings.iends_with(., "ccsend.com"))
 89  )
 90  // negating legit replies
 91  and not (
 92    (
 93      strings.istarts_with(subject.subject, "RE:")
 94      or strings.istarts_with(subject.subject, "FW:")
 95      or strings.istarts_with(subject.subject, "FWD:")
 96      or strings.istarts_with(subject.subject, "Automatic reply:")
 97      or regex.imatch(subject.subject,
 98                      '(\[[^\]]+\]\s?){0,3}(re|fwd?|automat.*)\s?:.*'
 99      )
100    )
101    and (length(headers.references) > 0 or headers.in_reply_to is not null)
102  )
103  // negate highly trusted sender domains unless they fail DMARC authentication
104  and (
105    (
106      sender.email.domain.root_domain in $high_trust_sender_root_domains
107      and not headers.auth_summary.dmarc.pass
108    )
109    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
110  )
111  and profile.by_sender().prevalence in ("new", "outlier", "rare")  
112attack_types:
113  - "Credential Phishing"
114tactics_and_techniques:
115  - "Free email provider"
116  - "Open redirect"
117  - "Social engineering"
118detection_methods:
119  - "Content analysis"
120  - "Header analysis"
121  - "QR code analysis"
122  - "Sender analysis"
123id: "8c5e8e4c-c610-5ece-b82a-214c637cba09"