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Low Severity

Attachment: Any HTML file (unsolicited)

Description

Potential HTML smuggling attacks in unsolicited messages. Use if passing HTML files is not normal behavior in your environment. This rule may be expanded to inspect HTML attachments for suspicious code.

Sublime Security
Created Aug 17th, 2023 • Last updated Nov 3rd, 2025
Source
type.inbound
and any(attachments,
        .file_extension in~ ('htm', 'html') or .file_type == "html"
)
and (
  not profile.by_sender().solicited
  or profile.by_sender().any_messages_malicious_or_spam
)
and not profile.by_sender().any_messages_benign

// negate highly trusted sender domains unless they fail DMARC authentication or DMARC is missing
and not (
  sender.email.domain.root_domain in $high_trust_sender_root_domains
  and coalesce(headers.auth_summary.dmarc.pass, false)
)
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