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47 changes: 47 additions & 0 deletions detection-rules/Suspicious_TA4903_PDF.yml
Original file line number Diff line number Diff line change
@@ -0,0 +1,47 @@
name: "USDA Bid Invitation Impersonation"
description: "Detects messages claiming to be from USDA containing bid invitations with macro-enabled attachments or PDFs. Validates USDA-related content through OCR and natural language analysis."
type: "rule"
severity: "medium"
references:
- "https://www.proofpoint.com/uk/blog/threat-insight/ta4903-actor-spoofs-us-government-small-businesses-phishing-bec-bids"
source: |
type.inbound
and length(attachments) == 1
and all(attachments,
.file_extension in~ $file_extensions_macros or .file_type == "pdf"
)
and strings.icontains(body.current_thread.text, "bid")
and (
strings.icontains(subject.subject, 'invitation to bid')
or any(attachments, strings.icontains(.file_name, 'usda'))
)
and strings.icontains(sender.email.domain.domain, "usda")
and (
any(ml.nlu_classifier(body.current_thread.text).entities,
.text == "usda" and .name in ("sender", "org")
)
and any(attachments,
any(file.explode(.),
any(ml.nlu_classifier(.scan.ocr.raw).entities,
strings.icontains(.text, "Agriculture")
)
)
)
)


attack_types:
- "BEC/Fraud"
tactics_and_techniques:
- "Impersonation: Brand"
- "PDF"
- "Macros"
- "Social engineering"
detection_methods:
- "Content analysis"
- "File analysis"
- "Header analysis"
- "Natural Language Understanding"
- "Optical Character Recognition"
- "Sender analysis"
id: "34eb9493-f74b-535a-8e21-bb37ca69b7f4"