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Enhance impersonation detection for Microsoft Teams #3491

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Enhance impersonation detection for Microsoft Teams #3491

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46 changes: 26 additions & 20 deletions detection-rules/impersonation_microsoft.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,8 @@ source: |
and strings.ilike(body.current_thread.text, "*microsoft*")
)
or regex.icontains(body.current_thread.text,
".*reach you.{0,20}Microsoft Teams"
".*reach you.{0,20}Microsoft Teams",
"microsoft teams.*meeting (recording|event)"
)
or strings.ilike(sender.display_name, '*new activity in Teams*')
or strings.icontains(strings.replace_confusables(sender.display_name),
Expand All @@ -52,19 +53,22 @@ source: |
"[MḾṀṂⱮМḿṁṃᵯⱮ𝐌𝑀][iíìîïīĭĩįıɪɨᵢⁱ𝐢𝑖][rŕŗřȑȓɾᵣⁿʳ𝐫𝑟][cćĉċčçƈȼ𝐜𝑐][oóòôõöøōŏőɵₒᵒº𝐨𝑜][sśŝšșşʂᵴˢˢ𝐬𝑠][oóòôõöøōŏőɵₒᵒº𝐨𝑜][fḟƒᵮᶠ𝐟𝑓][tťțţᵵₜᵗᵗ𝐭𝑡]" // [sic]
)
)
and sender.email.domain.root_domain not in~ (
'microsoft.com',
'microsoftstoreemail.com',
'microsoftsupport.com',
'office.com',
'teams-events.com',
'qualtrics-research.com',
'skype.com',
'azureadnotifications.us',
'microsoftonline.us',
'mail.microsoft',
'office365.com',
'microsoftadvertising.com'
and (
sender.email.domain.root_domain not in~ (
'microsoft.com',
'microsoftstoreemail.com',
'microsoftsupport.com',
'office.com',
'teams-events.com',
'qualtrics-research.com',
'skype.com',
'azureadnotifications.us',
'microsoftonline.us',
'mail.microsoft',
'office365.com',
'microsoftadvertising.com'
)
or not sender.email.domain.valid
)
and not (
sender.email.domain.domain in~ (
Expand All @@ -74,13 +78,15 @@ source: |
and headers.auth_summary.dmarc.pass
)
and (
profile.by_sender().prevalence in ("new", "outlier")
or (
profile.by_sender().any_messages_malicious_or_spam
and not profile.by_sender().any_messages_benign
(
profile.by_sender().prevalence in ("new", "outlier")
or (
profile.by_sender().any_messages_malicious_or_spam
and not profile.by_sender().any_messages_benign
)
)
)

or not sender.email.domain.valid
)
// negate legitimate Office 365 bouncebacks
and not (
all(attachments,
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