Detection rules › Sublime MQL
Attachment: Archive with embedded EXE file
Recursively scans files and archives to detect embedded EXE files (with an MZ header). According to The Record, on June 7, 2021, the Ukrainian Secret Service attributed an attack that used this technique to the "special services of the Russian Federation". The spear-phishing operation urged recipients to download a RAR archive included in the email, which, when decompressed, would drop an EXE file with a double extension (filename.pdf.exe) that tried to pass as a PDF file.
Threat classification
Sublime's own taxonomy (not MITRE ATT&CK).
| Category | Values |
|---|---|
| Attack types | Malware/Ransomware |
| Tactics and techniques | Evasion |
Event coverage
| Message attribute |
|---|
| attachments (collection) |
| type |
Rule body MQL
type.inbound
and any(attachments,
(
.file_extension in~ $file_extensions_common_archives
or .file_type == "rar"
)
and any(file.explode(.),
// the YARA scanner alone can be a bit unreliable,
// it's matched on MZ strings in a text file before
any(.flavors.yara, . == "mz_file")
and strings.starts_with(.flavors.mime, "application")
)
)
Detection logic
Scope: inbound message.
Recursively scans files and archives to detect embedded EXE files (with an MZ header). According to The Record, on June 7, 2021, the Ukrainian Secret Service attributed an attack that used this technique to the "special services of the Russian Federation". The spear-phishing operation urged recipients to download a RAR archive included in the email, which, when decompressed, would drop an EXE file with a double extension (filename.pdf.exe) that tried to pass as a PDF file.
- inbound message
any of
attachmentswhere all hold:any of:
- .file_extension in $file_extensions_common_archives
- .file_type is 'rar'
any of
file.explode(.)where all hold:any of
.flavors.yarawhere:- . is 'mz_file'
- .flavors.mime starts with 'application'
Inspects: attachments[].file_extension, attachments[].file_type, type.inbound. Sensors: file.explode, strings.starts_with. Reference lists: $file_extensions_common_archives.
Indicators matched (3)
| Field | Match | Value |
|---|---|---|
attachments[].file_type | equals | rar |
file.explode(attachments[])[].flavors.yara[] | equals | mz_file |
strings.starts_with | prefix | application |