sublimemediumRule

Evasion: Hidden content divs from freemail sender

Detects inbound messages from freemail senders containing multiple hidden HTML div elements with specific styling properties (display:none, opacity:0, zero dimensions) that are commonly used to evade content filtering and detection systems.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1036 T1027

defense-evasion

Detection Query

type.inbound
and sender.email.domain.root_domain in $free_email_providers
and strings.count(body.html.raw,
                  '<div style="display:none;opacity:0;width:0;height:0;overflow:hidden" aria-hidden="true">'
) >= 3

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Evasion: Hidden content divs from freemail sender"
description: "Detects inbound messages from freemail senders containing multiple hidden HTML div elements with specific styling properties (display:none, opacity:0, zero dimensions) that are commonly used to evade content filtering and detection systems."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and sender.email.domain.root_domain in $free_email_providers
  and strings.count(body.html.raw,
                    '<div style="display:none;opacity:0;width:0;height:0;overflow:hidden" aria-hidden="true">'
  ) >= 3
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "Free email provider"
detection_methods:
  - "HTML analysis"
  - "Content analysis"
  - "Sender analysis"
id: "15548316-19ca-5f81-91d4-98a877bae765"