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Testing word-boundary Cyrillic homoglyph detection #4639

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Testing word-boundary Cyrillic homoglyph detection #4639

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fdb438c
Expand Cyrillic detection with OR logic for maximum coverage
IndiaAce Jun 9, 2026
26b89d7
Auto-format MQL and add rule IDs
Jun 9, 2026
d319773
Exempt historical mimic test canonicals 402455 and 936366
IndiaAce Jun 9, 2026
126f390
Replace OR logic with word-boundary detection for Cyrillic homoglyphs
IndiaAce Jun 9, 2026
a2ecb75
Auto-format MQL and add rule IDs
Jun 9, 2026
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8 changes: 5 additions & 3 deletions detection-rules/link_cyrillic_substitutions_unsolicited.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,9 +15,12 @@ source: |
)
)

// display name or subject contains Cyrillic vowels in addition to standard letters
// display name or subject contains Cyrillic/Greek confusables within the same word as Latin
// Both scripts must appear in a single whitespace-delimited token (true homoglyph substitution)
and any([subject.subject, sender.display_name],
regex.icontains(., '(а|е|и|о|у)') and regex.icontains(., '[a-z]')
regex.contains(.,
'[a-zA-Z][^\s]*[\x{430}\x{435}\x{438}\x{43e}\x{443}\x{440}\x{441}\x{445}\x{456}\x{410}\x{412}\x{415}\x{41a}\x{41c}\x{41d}\x{41e}\x{420}\x{421}\x{422}\x{425}\x{391}\x{392}\x{395}\x{396}\x{397}\x{399}\x{39a}\x{39c}\x{39d}\x{39f}\x{3a1}\x{3a4}\x{3a5}\x{3a7}\x{3bf}]|[\x{430}\x{435}\x{438}\x{43e}\x{443}\x{440}\x{441}\x{445}\x{456}\x{410}\x{412}\x{415}\x{41a}\x{41c}\x{41d}\x{41e}\x{420}\x{421}\x{422}\x{425}\x{391}\x{392}\x{395}\x{396}\x{397}\x{399}\x{39a}\x{39c}\x{39d}\x{39f}\x{3a1}\x{3a4}\x{3a5}\x{3a7}\x{3bf}][^\s]*[a-zA-Z]'
)
)

// and the senders tld or return path is not "ru"
Expand All @@ -40,7 +43,6 @@ source: |
)
)
and not profile.by_sender().any_messages_benign

tags:
- "Attack surface reduction"
attack_types:
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7 changes: 5 additions & 2 deletions detection-rules/link_suspicious_subject_with_cyrillic_substitutions.yml
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Expand Up @@ -6,9 +6,12 @@ source: |
type.inbound
and 0 < length(body.links) < 10

// display name or subject contains confusable vowels
// display name or subject contains Cyrillic/Greek confusables within the same word as Latin
// Both scripts must appear in a single whitespace-delimited token (true homoglyph substitution)
and any([subject.subject, sender.display_name],
regex.icontains(., '(а|е|и|о|у)')
regex.contains(.,
'[a-zA-Z][^\s]*[\x{430}\x{435}\x{438}\x{43e}\x{443}\x{440}\x{441}\x{445}\x{456}\x{410}\x{412}\x{415}\x{41a}\x{41c}\x{41d}\x{41e}\x{420}\x{421}\x{422}\x{425}\x{391}\x{392}\x{395}\x{396}\x{397}\x{399}\x{39a}\x{39c}\x{39d}\x{39f}\x{3a1}\x{3a4}\x{3a5}\x{3a7}\x{3bf}]|[\x{430}\x{435}\x{438}\x{43e}\x{443}\x{440}\x{441}\x{445}\x{456}\x{410}\x{412}\x{415}\x{41a}\x{41c}\x{41d}\x{41e}\x{420}\x{421}\x{422}\x{425}\x{391}\x{392}\x{395}\x{396}\x{397}\x{399}\x{39a}\x{39c}\x{39d}\x{39f}\x{3a1}\x{3a4}\x{3a5}\x{3a7}\x{3bf}][^\s]*[a-zA-Z]'
)
)

// and suspicious subject
Expand Down