sublimehighRule

Attachment: HTML with JavaScript functions for HTTP requests

This rule identifies HTML attachments which contain multiple references to JavaScript functions that support making HTTP requests. This has been observed in phishing campaigns to load remote payloads into otherwise benign HTML attachments.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1036 T1027 T1059

defense-evasionexecution

Detection Query

type.inbound
and not profile.by_sender().solicited
// not high trust sender domains
and not (
  sender.email.domain.root_domain in $high_trust_sender_root_domains
  and coalesce(headers.auth_summary.dmarc.pass, false)
)
and any(attachments,
        .file_extension in~ ("html", "htm", "shtml", "dhtml")
        and 3 of (
          strings.icontains(file.parse_html(.).raw, '.replace'),
          strings.icontains(file.parse_html(.).raw, 'XMLHttpRequest'),
          strings.icontains(file.parse_html(.).raw, 'onreadystate'),
          strings.icontains(file.parse_html(.).raw, 'GET'),
          strings.icontains(file.parse_html(.).raw, 'send()'),
          strings.icontains(file.parse_html(.).raw, 'responseText'),
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: HTML with JavaScript functions for HTTP requests"
description: "This rule identifies HTML attachments which contain multiple references to JavaScript functions that support making HTTP requests. This has been observed in phishing campaigns to load remote payloads into otherwise benign HTML attachments."
type: "rule"
severity: "high"
source: |
  type.inbound
  and not profile.by_sender().solicited
  // not high trust sender domains
  and not (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and coalesce(headers.auth_summary.dmarc.pass, false)
  )
  and any(attachments,
          .file_extension in~ ("html", "htm", "shtml", "dhtml")
          and 3 of (
            strings.icontains(file.parse_html(.).raw, '.replace'),
            strings.icontains(file.parse_html(.).raw, 'XMLHttpRequest'),
            strings.icontains(file.parse_html(.).raw, 'onreadystate'),
            strings.icontains(file.parse_html(.).raw, 'GET'),
            strings.icontains(file.parse_html(.).raw, 'send()'),
            strings.icontains(file.parse_html(.).raw, 'responseText'),
          )
  )

attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "Scripting"
detection_methods:
  - "Content analysis"
  - "HTML analysis"
  - "Javascript analysis"
  - "File analysis"
id: "01e679fd-6c5a-542f-b98b-1b8de7132311"