• Sublime Core Feed
Medium Severity

Sharepoint Link Likely Unrelated to Sender

Labels

BEC/Fraud
Credential Phishing
Impersonation: Employee
Lookalike domain
OneNote
PDF
Social engineering
URL analysis
Sender analysis
Header analysis
HTML analysis

Description

Detects when a sender links to a Sharepoint file where the subdomain significantly differs from the sender's domain. The rule checks for OneNote, PDF, or unknown file types and includes various domain validation checks.

References

No references.

Sublime Security
Created Mar 12th, 2025 • Last updated Mar 12th, 2025
Feed Source
Sublime Core Feed
Source
GitHub
type.inbound
and any(beta.ml_topic(body.html.display_text).topics,
        .name == "File Sharing and Cloud Services" and .confidence == "high"
)
and 0 < length(body.links) < 10
and length(body.html.display_text) < 2000
and any(filter(body.links, .href_url.domain.root_domain == 'sharepoint.com'),
        // Normalize Levenshtein distance by string length (0 = identical, 0.7+ = different)
        // Working with what we have in MQL, considering we dont have max() or any other forms of string distancing
        (
          (
            strings.iends_with(.href_url.domain.subdomain,
                               '-my'
            ) // common Sharepoint subdomain suffix
            and (
              (
                strings.ilevenshtein(.href_url.domain.subdomain,
                                     sender.email.domain.sld
                ) - 3 // subtract aforementioned suffix for more accurate calculation
              ) / (
                (
                  (length(.href_url.domain.subdomain) - 3) + length(sender.email.domain.sld
                  )
 + (
                    (
                      (length(.href_url.domain.subdomain) - 3) - length(sender.email.domain.sld
                      )
                    ) + (
                      length(sender.email.domain.sld) - (
                        length(.href_url.domain.subdomain) - 3
                      )
                    )
                  )
                ) / 2.0 // to ensure we keep the result as a float
              )
            ) > 0.7 // customizable threshold
          )
          or (
            not strings.iends_with(.href_url.domain.subdomain,
                                   '-my'
            ) // no suffix, continue with original calculation
            and (
              strings.ilevenshtein(.href_url.domain.subdomain,
                                   sender.email.domain.sld
              ) / (
                (
                  length(.href_url.domain.subdomain) + length(sender.email.domain.sld
                  )
 + (
                    (
                      length(.href_url.domain.subdomain) - length(sender.email.domain.sld
                      )
                    ) + (
                      length(sender.email.domain.sld) - length(.href_url.domain.subdomain
                      )
                    )
                  )
                ) / 2.0 // to ensure we keep the result as a float
              )
            ) > 0.7 // customizable threshold
          )
        )
        and not strings.icontains(.href_url.path, sender.email.local_part)
        and not any($org_slds, strings.icontains(..href_url.domain.subdomain, .))

        // it is either a OneNote or PDF file, or unknown
        and (
          strings.icontains(.href_url.path, '/:o:/p')
          or strings.icontains(.href_url.path, '/:b:/p')
          or strings.icontains(.href_url.path, '/:u:/p')
        )

)

// a way to negate long threads
// the full thread must be less than 6 times the length of the current thread
and length(body.html.inner_text) < 6 * length(body.current_thread.text)
and sender.email.domain.root_domain not in (
  "sharepoint.com",
  "sharepointonline.com"
)

// negate highly trusted sender domains unless they fail DMARC authentication
and (
  (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and not headers.auth_summary.dmarc.pass
  )
  or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)
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