sublimemediumRule

Attachment with unscannable encrypted zip (unsolicited)

Recursively scans files and archives to detect embedded ZIP files that are encrypted and could not be opened/scanned.

MITRE ATT&CK

T1566.001 T1204.002 T1486 T1027 T1573 T1036

defense-evasion

Detection Query

type.inbound
and any(attachments,
        (.file_type == "zip" or .file_extension == "zip")
        and any(file.explode(.),
                any(.flavors.yara, . == 'encrypted_zip')
                and .scan.encrypted_zip.cracked_password == null
        )
)
and (
  not profile.by_sender().solicited
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

References

https://www.zdnet.com/article/this-phishing-email-contains-a-password-protected-file-dont-open-it/

Raw Content

name: "Attachment with unscannable encrypted zip (unsolicited)"
description: |
  Recursively scans files and archives to detect embedded ZIP files
  that are encrypted and could not be opened/scanned.
references:
  - "https://www.zdnet.com/article/this-phishing-email-contains-a-password-protected-file-dont-open-it/"
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          (.file_type == "zip" or .file_extension == "zip")
          and any(file.explode(.),
                  any(.flavors.yara, . == 'encrypted_zip')
                  and .scan.encrypted_zip.cracked_password == null
          )
  )
  and (
    not profile.by_sender().solicited
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_messages_benign
    )
  )
attack_types:
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Encryption"
  - "Evasion"
detection_methods:
  - "Archive analysis"
  - "File analysis"
  - "Sender analysis"
  - "YARA"
id: "529d4a9a-ffa7-5a53-a065-df244ec67e7a"