sublimehighRule

Attachment: HTML smuggling 'body onload' with high entropy and suspicious text

Potential HTML Smuggling. This rule inspects HTML attachments that contain "body unload", high entropy, and suspicious text.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1204.002 T1486 T1036 T1027 T1059

defense-evasionexecution

Detection Query

type.inbound
and any(attachments,
        (
          .file_extension in~ ("html", "htm", "shtml", "dhtml", "xhtml")
          or (
            .file_extension is null
            and .file_type == "unknown"
            and .content_type == "application/octet-stream"
          )
          or .file_extension in~ $file_extensions_common_archives
          or .file_type == "html"
          or .content_type == "text/html"
        )
        and any(file.explode(.),
                .scan.entropy.entropy >= 5
                and any(.scan.strings.strings,
                        strings.ilike(., "*body onload*")
                )
                and any(.scan.strings.strings,
                        regex.icontains(., 'data:image/.*;base64')
                )
                and any(.scan.strings.strings,
                        strings.ilike(., "*document pass*")
                )
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: HTML smuggling 'body onload' with high entropy and suspicious text"
description: |
  Potential HTML Smuggling. This rule inspects HTML attachments that contain "body unload", high entropy, and suspicious text.
type: "rule"
severity: "high"
source: |
  type.inbound
  and any(attachments,
          (
            .file_extension in~ ("html", "htm", "shtml", "dhtml", "xhtml")
            or (
              .file_extension is null
              and .file_type == "unknown"
              and .content_type == "application/octet-stream"
            )
            or .file_extension in~ $file_extensions_common_archives
            or .file_type == "html"
            or .content_type == "text/html"
          )
          and any(file.explode(.),
                  .scan.entropy.entropy >= 5
                  and any(.scan.strings.strings,
                          strings.ilike(., "*body onload*")
                  )
                  and any(.scan.strings.strings,
                          regex.icontains(., 'data:image/.*;base64')
                  )
                  and any(.scan.strings.strings,
                          strings.ilike(., "*document pass*")
                  )
          )
  )
attack_types:
  - "Credential Phishing"
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Evasion"
  - "HTML smuggling"
  - "Scripting"
detection_methods:
  - "Archive analysis"
  - "Content analysis"
  - "File analysis"
  - "HTML analysis"
id: "329ac12d-f74e-577c-936c-1db80ccf860e"