sublimehighRule

Attachment: HTML smuggling with embedded base64-encoded ISO

HTML attachment contains a base-64 encoded ISO. This is a known TTP for multiple threat actors.

MITRE ATT&CK

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

defense-evasion

Detection Query

type.inbound
and any(attachments,
        (
          .file_extension in~ ("html", "htm")
          or .file_extension in~ $file_extensions_common_archives
          or .file_type == "html"
        )
        and any(file.explode(.),
                any(.scan.strings.strings,
                    strings.ilike(.,
                                  // Base64 encoded ISOs
                                  "*SVNPIDk2NjAvSEZT*",
                                  "*MTk5MyBFLllPVU5HREFMRQ*",
                                  // Reversed base64 encoded ISOs
                                  "*TZESvAjN2kDIPNVS*",
                                  "*QRMFERH5UVPllLFByM5kTM*"
                    )
                )
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

References

Raw Content

name: "Attachment: HTML smuggling with embedded base64-encoded ISO"
description: |
  HTML attachment contains a base-64 encoded ISO. This is a known TTP for multiple threat actors.
references:
  - "https://delivr.to/payloads?id=cf6c9867-4358-4b3b-b7eb-3432ac39e71d"
  - "https://playground.sublimesecurity.com?id=78587abf-1027-4c6c-9edf-c1bd928de97a"
type: "rule"
severity: "high"
source: |
  type.inbound
  and any(attachments,
          (
            .file_extension in~ ("html", "htm")
            or .file_extension in~ $file_extensions_common_archives
            or .file_type == "html"
          )
          and any(file.explode(.),
                  any(.scan.strings.strings,
                      strings.ilike(.,
                                    // Base64 encoded ISOs
                                    "*SVNPIDk2NjAvSEZT*",
                                    "*MTk5MyBFLllPVU5HREFMRQ*",
                                    // Reversed base64 encoded ISOs
                                    "*TZESvAjN2kDIPNVS*",
                                    "*QRMFERH5UVPllLFByM5kTM*"
                      )
                  )
          )
  )
attack_types:
  - "Credential Phishing"
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Evasion"
  - "HTML smuggling"
  - "ISO"
detection_methods:
  - "Archive analysis"
  - "Content analysis"
  - "File analysis"
  - "HTML analysis"
  - "Sender analysis"
id: "294ecd2d-bc98-5a67-850a-60a1a29aea76"