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Detection rules › Sublime MQL

Link to auto-downloaded DMG in encrypted zip

Severity
high
Type
rule
Source
github.com/sublime-security/sublime-rules

A link in the body of the message downloads an encrypted zip that contains a DMG file. This technique has been observed ITW to deliver Meta Stealer, Atomic Stealer, and other MacOS malware. Notably, in some instances, the attacker poses as a recruiter and initiates back and forth conversation with the recipient.

Threat classification

Sublime's own taxonomy (not MITRE ATT&CK).

CategoryValues
Attack typesMalware/Ransomware
Tactics and techniquesEncryption, Evasion, Social engineering

Event coverage

Message attribute
body
headers.auth_summary
sender.email
type

Rule body MQL

type.inbound
and any(body.links,
        any(ml.link_analysis(.).files_downloaded,
            any(file.explode(.),
                (
                  any(.flavors.yara, . == "encrypted_zip")
                  and any(.scan.zip.all_paths,
                          any([".dmg"], strings.ends_with(.., .))
                  )
                )
            )
        )
)
and (
  profile.by_sender().prevalence != "common"
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)

// negate highly trusted sender domains unless they fail DMARC authentication
and (
  (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and not headers.auth_summary.dmarc.pass
  )
  or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)

Detection logic

Scope: inbound message.

A link in the body of the message downloads an encrypted zip that contains a DMG file. This technique has been observed ITW to deliver Meta Stealer, Atomic Stealer, and other MacOS malware. Notably, in some instances, the attacker poses as a recruiter and initiates back and forth conversation with the recipient.

  1. inbound message
  2. any of body.links where:
    • any of ml.link_analysis(.).files_downloaded where:
      • any of file.explode(.) where all hold:
        • any of .flavors.yara where:
          • . is 'encrypted_zip'
        • any of .scan.zip.all_paths where:
          • any of ['.dmg'] where:
            • strings.ends_with(.)
  3. any of:
    • profile.by_sender().prevalence is not 'common'
    • all of:
      • profile.by_sender().any_messages_malicious_or_spam
      • not:
        • profile.by_sender().any_messages_benign
  4. any of:
    • all of:
      • sender.email.domain.root_domain in $high_trust_sender_root_domains
      • not:
        • headers.auth_summary.dmarc.pass
    • sender.email.domain.root_domain not in $high_trust_sender_root_domains

Inspects: body.links, headers.auth_summary.dmarc.pass, sender.email.domain.root_domain, type.inbound. Sensors: file.explode, ml.link_analysis, profile.by_sender, strings.ends_with. Reference lists: $high_trust_sender_root_domains.

Indicators matched (1)

FieldMatchValue
file.explode(ml.link_analysis(body.links[]).files_downloaded[])[].flavors.yara[]equalsencrypted_zip