sublimemediumRule

Attachment: Archive with embedded CHM file

Recursively scans files and archives to detect embedded CHM (Microsoft Compiled HTML Help) files. According to CERT-UA, on March 7, 2022, phishing attacks targeted state organizations of Ukraine using Zip files with embedded CHM documents, which themselves contained malicious VBScript inside a .htm file. The activity is associated with UNC1151, according to CERT-UA.

MITRE ATT&CK

T1566.001 T1204.002 T1486 T1036 T1027

defense-evasion

Detection Query

type.inbound
and any(attachments,
        .file_extension in~ $file_extensions_common_archives
        and any(file.explode(.), .file_extension =~ "chm")
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

References

https://cert.gov.ua/article/37626

Raw Content

name: "Attachment: Archive with embedded CHM file"
description: |
  Recursively scans files and archives to detect embedded CHM (Microsoft Compiled HTML Help) files.

  According to CERT-UA, on March 7, 2022, phishing attacks targeted state organizations of Ukraine
  using Zip files with embedded CHM documents, which themselves contained malicious VBScript inside a .htm file.
  The activity is associated with UNC1151, according to CERT-UA.
references:
  - "https://cert.gov.ua/article/37626"
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          .file_extension in~ $file_extensions_common_archives
          and any(file.explode(.), .file_extension =~ "chm")
  )
attack_types:
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Evasion"
detection_methods:
  - "Archive analysis"
  - "File analysis"
id: "5280e94d-592b-5d80-b548-b0e2ad4c9eae"