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Detection rules › Sublime MQL

Attachment: PDF with fake invoice using suspicious font sizing

Severity
medium
Type
rule
Source
github.com/sublime-security/sublime-rules

PDF attachment contains a fake invoice with suspicious font size patterns and unique image sizes, typically used in fraudulent billing schemes.

Threat classification

Sublime's own taxonomy (not MITRE ATT&CK).

CategoryValues
Attack typesBEC/Fraud, Callback Phishing
Tactics and techniquesPDF, Social engineering

Event coverage

Message attribute
attachments (collection)
type

Rule body MQL

type.inbound
and any(filter(attachments, .file_type == "pdf"),
        any(file.explode(.),
            any(.scan.yara.matches,
                .name == "pdf_fake_invoice_image_font_sizes"
            )
        )
)

Detection logic

Scope: inbound message.

PDF attachment contains a fake invoice with suspicious font size patterns and unique image sizes, typically used in fraudulent billing schemes.

  1. inbound message
  2. any of filter(attachments) where:
    • any of file.explode(.) where:
      • any of .scan.yara.matches where:
        • .name is 'pdf_fake_invoice_image_font_sizes'

Inspects: attachments[].file_type, type.inbound. Sensors: file.explode.

Indicators matched (2)

FieldMatchValue
attachments[].file_typeequalspdf
file.explode(filter(attachments)[])[].scan.yara.matches[].nameequalspdf_fake_invoice_image_font_sizes