Medium Severity

Attachment: Hex-encoded recipient email in URL fragment

Labels

Credential Phishing

BEC/Fraud

Description

Detects non-ICS attachments (PDFs, Office docs, HTML, etc.) that embed a URL whose fragment contains the recipient's email address encoded in hexadecimal. This technique is used to personalize or track clicks on malicious links delivered via file attachments rather than inline in the message body. Observed samples largely spoof financial or invoicing correspondence—such as invoice notices, AR aging reports, and cashflow or change-order updates—to lure recipients into opening the attachment and following the embedded link, often leading to credential phishing.

References

No references.

Sublime Security

Created Sep 16th, 2026 • Last updated Sep 16th, 2026

Feed Source

Sublime Core Feed

Source

GitHub

type.inbound
and any(attachments,
        not (
          .file_type == "ics"
          or .file_extension == "ics"
          or .content_type in ("application/ics", "text/calendar")
        )
        and any(file.explode(.),
                any(.scan.url.urls,
                    strings.decode_hex(.fragment) == recipients.to[0].email.email
                )
        )
)

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