VIP / Executive impersonation (strict match, untrusted)

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

Sender display name matches the display name of a user in the $org_vips list, and the sender has never been seen before. The $org_vips list must first be manually connected to a VIP group of your upstream provider (Google Workspace and Microsoft 365 only) in order for this rule to work. Once connected, the list will be automatically synced and kept up-to-date. For more information, see the $org_vips documentation: https://docs.sublimesecurity.com/docs/configure-org_vips-list This rule is recommended to be used on a relatively small list of VIPs, and is meant to reduce attack surface by detecting any message that matches the protected list of display names from a first-time or unsolicited sender. Additional rule logic can be added to look for suspicious subjects, suspicious links, etc.

Threat classification

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

Category	Values
Attack types	BEC/Fraud
Tactics and techniques	Impersonation: VIP

Event coverage

Message attribute
attachments (collection)
body.current_thread
headers (collection)
headers.auth_summary
headers.reply_to (collection)
mailbox
recipients
sender
sender.email
type

Rule body MQL

type.inbound
and (
  // the display name matches a name on the orgs vip list
  any($org_vips, .display_name =~ sender.display_name)
  // or the display name starts with the name on the orgs vip list
  or (
    any($org_vips,
        strings.istarts_with(sender.display_name, .display_name)
        // and it is longer than just their name (eg. John Doe CEO)
        and length(sender.display_name) > length(.display_name)
    )
    // and we have confidence it's BEC
    and any(ml.nlu_classifier(body.current_thread.text).intents,
            .name == "bec" and .confidence == "high"
    )
  )
)
and (
  // ignore personal <> work emails
  // where the sender and mailbox's display name are the same
  length(recipients.to) > 0
  or length(recipients.cc) > 0
  or sender.display_name != mailbox.display_name
)
// bounce-back negations
and not strings.like(sender.email.local_part,
                     "*postmaster*",
                     "*mailer-daemon*",
                     "*administrator*"
)
and not any(attachments,
            .content_type in (
              "message/rfc822",
              "message/delivery-status",
              "text/calendar"
            )
)
and (
  (
    profile.by_sender_email().prevalence in ("new", "outlier")
    and not profile.by_sender_email().solicited
  )
  or (
    profile.by_sender_email().any_messages_malicious_or_spam
    and not profile.by_sender_email().any_messages_benign
  )
  // mismatched reply-to with unsoliticed reply-to address
  or (
    length(headers.reply_to) > 0
    and (sender.email.email not in map(headers.reply_to, .email.email))
    // negate reply-to addresses that are within the org domain
    and not all(headers.reply_to,
                .email.domain.domain in $org_domains
                or .email.domain.root_domain in $org_domains
    )
    //
    // This rule makes use of a beta feature and is subject to change without notice
    // using the beta feature in custom rules is not suggested until it has been formally released
    //
    and not beta.profile.by_reply_to().solicited
    and beta.profile.by_reply_to().prevalence != "common"
  )
)
and (
  (
    sender.email.domain.root_domain in $org_domains
    and not headers.auth_summary.dmarc.pass
  )
  or sender.email.domain.root_domain not in $org_domains
)
and not profile.by_sender_email().any_messages_benign

Detection logic

Scope: inbound message.

inbound message
any of:
- any of $org_vips where:
  - .display_name is sender.display_name
- all of:
  - any of $org_vips where all hold:
    
    strings.istarts_with(sender.display_name)
    length(sender.display_name) > length(.display_name)
  - any of ml.nlu_classifier(body.current_thread.text).intents where all hold:
    
    .name is 'bec'
    .confidence is 'high'
any of:
- length(recipients.to) > 0
- length(recipients.cc) > 0
- sender.display_name is not mailbox.display_name
not:
- sender.email.local_part matches any of 3 patterns
  - *postmaster*
  - *mailer-daemon*
  - *administrator*
not:
- any of attachments where:
  - .content_type in ('message/rfc822', 'message/delivery-status', 'text/calendar')
any of:
- all of:
  - profile.by_sender_email().prevalence in ('new', 'outlier')
  - not:
    
    profile.by_sender_email().solicited
- all of:
  - profile.by_sender_email().any_messages_malicious_or_spam
  - not:
    
    profile.by_sender_email().any_messages_benign
- all of:
  - length(headers.reply_to) > 0
  - sender.email.email not in map(headers.reply_to, .email.email)
  - not:
    
    all of headers.reply_to where any holds:
    
    .email.domain.domain in $org_domains
    .email.domain.root_domain in $org_domains
  - not:
    
    beta.profile.by_reply_to().solicited
  - beta.profile.by_reply_to().prevalence is not 'common'
any of:
- all of:
  - sender.email.domain.root_domain in $org_domains
  - not:
    
    headers.auth_summary.dmarc.pass
- sender.email.domain.root_domain not in $org_domains
not:
- profile.by_sender_email().any_messages_benign

Inspects: attachments[].content_type, body.current_thread.text, headers.auth_summary.dmarc.pass, headers.reply_to, headers.reply_to[].email.domain.domain, headers.reply_to[].email.domain.root_domain, headers.reply_to[].email.email, mailbox.display_name, recipients.cc, recipients.to, sender.display_name, sender.email.domain.root_domain, sender.email.email, sender.email.local_part, type.inbound. Sensors: beta.profile.by_reply_to, ml.nlu_classifier, profile.by_sender_email, strings.istarts_with, strings.like. Reference lists: $org_domains, $org_vips.

Indicators matched (8)

Field	Match	Value
`ml.nlu_classifier(body.current_thread.text).intents[].name`	equals	`bec`
`ml.nlu_classifier(body.current_thread.text).intents[].confidence`	equals	`high`
`strings.like`	substring	`postmaster`
`strings.like`	substring	`mailer-daemon`
`strings.like`	substring	`administrator`
`attachments[].content_type`	member	`message/rfc822`
`attachments[].content_type`	member	`message/delivery-status`
`attachments[].content_type`	member	`text/calendar`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)