Brand impersonation: Outlook

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

Impersonation of Outlook.com. Senders with "outlook.com" in the subdomain have been observed sending fake account notifications.

Threat classification

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

Category	Values
Attack types	Credential Phishing
Tactics and techniques	Impersonation: Brand, Lookalike domain, Social engineering

Event coverage

Message attribute
sender.email
type

Rule body MQL

type.inbound
and regex.icontains(sender.email.domain.domain, '.*outlook.com.+')
// Negate legitimate outlook root domains
and sender.email.domain.root_domain not in (
  'outlook.com.au',
  'outlook.com.br',
  'outlook.com.ar',
  'outlook.at',
  'outlook.be',
  'outlook.cl',
  'outlook.cz',
  'outlook.dk',
  'outlook.fr',
  'outlook.de',
  'outlook.com.gr',
  'outlook.co.il',
  'outlook.in',
  'outlook.co.id',
  'outlook.ie',
  'outlook.it',
  'outlook.hu',
  'outlook.jp',
  'outlook.kr',
  'outlook.lv',
  'outlook.my',
  'outlook.co.nz',
  'outlook.com.pe',
  'outlook.ph',
  'outlook.pt',
  'outlook.sa',
  'outlook.sg',
  'outlook.sk',
  'outlook.es',
  'outlook.co.th',
  'outlook.com.tr',
  'outlook.com.vn'
)
and sender.email.email not in $recipient_emails

Detection logic

Scope: inbound message.

Impersonation of Outlook.com. Senders with "outlook.com" in the subdomain have been observed sending fake account notifications.

inbound message
sender.email.domain.domain matches '.*outlook.com.+'
sender.email.domain.root_domain not in ('outlook.com.au', 'outlook.com.br', 'outlook.com.ar', 'outlook.at', 'outlook.be', 'outlook.cl', 'outlook.cz', 'outlook.dk', 'outlook.fr', 'outlook.de', 'outlook.com.gr', 'outlook.co.il', 'outlook.in', 'outlook.co.id', 'outlook.ie', 'outlook.it', 'outlook.hu', 'outlook.jp', 'outlook.kr', 'outlook.lv', 'outlook.my', 'outlook.co.nz', 'outlook.com.pe', 'outlook.ph', 'outlook.pt', 'outlook.sa', 'outlook.sg', 'outlook.sk', 'outlook.es', 'outlook.co.th', 'outlook.com.tr', 'outlook.com.vn')
sender.email.email not in $recipient_emails

Inspects: sender.email.domain.domain, sender.email.domain.root_domain, sender.email.email, type.inbound. Sensors: regex.icontains. Reference lists: $recipient_emails.

Indicators matched (33)

Field	Match	Value
`regex.icontains`	regex	`.*outlook.com.+`
`sender.email.domain.root_domain`	member	`outlook.com.au`
`sender.email.domain.root_domain`	member	`outlook.com.br`
`sender.email.domain.root_domain`	member	`outlook.com.ar`
`sender.email.domain.root_domain`	member	`outlook.at`
`sender.email.domain.root_domain`	member	`outlook.be`
`sender.email.domain.root_domain`	member	`outlook.cl`
`sender.email.domain.root_domain`	member	`outlook.cz`
`sender.email.domain.root_domain`	member	`outlook.dk`
`sender.email.domain.root_domain`	member	`outlook.fr`
`sender.email.domain.root_domain`	member	`outlook.de`
`sender.email.domain.root_domain`	member	`outlook.com.gr`

21 more

`sender.email.domain.root_domain`	member	`outlook.co.il`
`sender.email.domain.root_domain`	member	`outlook.in`
`sender.email.domain.root_domain`	member	`outlook.co.id`
`sender.email.domain.root_domain`	member	`outlook.ie`
`sender.email.domain.root_domain`	member	`outlook.it`
`sender.email.domain.root_domain`	member	`outlook.hu`
`sender.email.domain.root_domain`	member	`outlook.jp`
`sender.email.domain.root_domain`	member	`outlook.kr`
`sender.email.domain.root_domain`	member	`outlook.lv`
`sender.email.domain.root_domain`	member	`outlook.my`
`sender.email.domain.root_domain`	member	`outlook.co.nz`
`sender.email.domain.root_domain`	member	`outlook.com.pe`
`sender.email.domain.root_domain`	member	`outlook.ph`
`sender.email.domain.root_domain`	member	`outlook.pt`
`sender.email.domain.root_domain`	member	`outlook.sa`
`sender.email.domain.root_domain`	member	`outlook.sg`
`sender.email.domain.root_domain`	member	`outlook.sk`
`sender.email.domain.root_domain`	member	`outlook.es`
`sender.email.domain.root_domain`	member	`outlook.co.th`
`sender.email.domain.root_domain`	member	`outlook.com.tr`
`sender.email.domain.root_domain`	member	`outlook.com.vn`

`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)