Callback phishing via Zelle Service Abuse

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

Callback phishing campaigns have been observed abusing Zelle services to send fraudulent payment requests with callback phishing contents.

Threat classification

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

Category	Values
Attack types	BEC/Fraud, Callback Phishing
Tactics and techniques	Evasion, Social engineering

Event coverage

Message attribute
body.current_thread
body.html
sender.email
subject
type

Rule body MQL

type.inbound
and length(attachments) == 0
and sender.email.domain.root_domain in ("zellepay.com")
and (
  // only seeing payment requests abused
  strings.ilike(body.html.display_text, "* requested*")
  // phone number in subject
  // the subject contains the seller's "name", attacks have been seen with the entire callback text in the seller's name
  or (
    regex.icontains(strings.replace_confusables(subject.subject),
                    '.*\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}.*'
    )
    or regex.icontains(strings.replace_confusables(subject.subject),
                       '.*\+[ilo0-9]{1,3}[ilo0-9]{10}.*'
    )
    // +12028001238
    or regex.icontains(strings.replace_confusables(subject.subject),
                       '.*[ilo0-9]{3}\.[ilo0-9]{3}\.[ilo0-9]{4}.*'
    )
    // 202-800-1238
    or regex.icontains(strings.replace_confusables(subject.subject),
                       '.*[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.*'
    )
    // (202) 800-1238
    or regex.icontains(strings.replace_confusables(subject.subject),
                       '.*\([ilo0-9]{3}\)[\s-]+[ilo0-9]{3}[\s-]+[ilo0-9]{4}.*'
    )
    // (202)-800-1238
    or regex.icontains(strings.replace_confusables(subject.subject),
                       '.*\([ilo0-9]{3}\)-[ilo0-9]{3}-[ilo0-9]{4}.*'
    )
    or ( // 8123456789
      regex.icontains(strings.replace_confusables(subject.subject),
                      '.*8[ilo0-9]{9}.*'
      )
      and regex.icontains(strings.replace_confusables(subject.subject),
                          '\+[1li]'
      )
    )
  )
)
and (
  (
    // icontains a phone number within the memo section (wrapped in quotes)
    (
      regex.icontains(strings.replace_confusables(body.current_thread.text),
                      '\".*\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}.*\"'
      )
      or regex.icontains(strings.replace_confusables(body.current_thread.text),
                         '\".*\+[ilo0-9]{1,3}[ilo0-9]{10}.*\"'
      )
      // +12028001238
      or regex.icontains(strings.replace_confusables(body.current_thread.text),
                         '\".*[ilo0-9]{3}\.[ilo0-9]{3}\.[ilo0-9]{4}.*\"'
      )
      // 202-800-1238
      or regex.icontains(strings.replace_confusables(body.current_thread.text),
                         '\".*[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.*\"'
      )
      // (202) 800-1238
      or regex.icontains(strings.replace_confusables(body.current_thread.text),
                         '\".*\([ilo0-9]{3}\)\s[ilo0-9]{3}-[ilo0-9]{4}.*\"'
      )
      // (202)-800-1238
      or regex.icontains(strings.replace_confusables(body.current_thread.text),
                         '\".*\([ilo0-9]{3}\)-[ilo0-9]{3}-[ilo0-9]{4}.*\"'
      )
      or ( // 8123456789
        regex.icontains(strings.replace_confusables(body.current_thread.text),
                        '\".*8[ilo0-9]{9}.*\"'
        )
        and regex.icontains(strings.replace_confusables(body.current_thread.text
                            ),
                            '\".*\+[1li].*\"'
        )
      )
    )
    and (
      (
        4 of (
          strings.ilike(body.html.inner_text, '*"*you did not*"*'),
          strings.ilike(body.html.inner_text, '*"*is not for*"*'),
          strings.ilike(body.html.inner_text, '*"*done by you*"*'),
          regex.icontains(body.html.inner_text, "\".*didn\'t ma[kd]e this.*\""),
          strings.ilike(body.html.inner_text, '*"*Fruad Alert*"*'),
          strings.ilike(body.html.inner_text, '*"*Fraud Alert*"*'),
          strings.ilike(body.html.inner_text, '*"*fraudulent*"*'),
          strings.ilike(body.html.inner_text, '*"*Zelle*"*'),
          strings.ilike(body.html.inner_text, '*"*subscription*"*'),
          strings.ilike(body.html.inner_text, '*"*antivirus*"*'),
          strings.ilike(body.html.inner_text, '*"*order*"*'),
          strings.ilike(body.html.inner_text, '*"*support*"*'),
          strings.ilike(body.html.inner_text, '*"*sincerely apologize*"*'),
          strings.ilike(body.html.inner_text, '*"*receipt*"*'),
          strings.ilike(body.html.inner_text, '*"*invoice*"*'),
          strings.ilike(body.html.inner_text, '*"*Purchase*"*'),
          strings.ilike(body.html.inner_text, '*"*transaction*"*'),
          strings.ilike(body.html.inner_text, '*"*Market*Value*"*'),
          strings.ilike(body.html.inner_text, '*"*BTC*"*'),
          strings.ilike(body.html.inner_text, '*"*call*"*'),
          strings.ilike(body.html.inner_text, '*"*get in touch with our*"*'),
          strings.ilike(body.html.inner_text, '*"*quickly inform*"*'),
          strings.ilike(body.html.inner_text, '*"*quickly reach*"*'),
          strings.ilike(body.html.inner_text,
                        '*"*detected unusual transactions*'
          ),
          strings.ilike(body.html.inner_text,
                        '*"*without your authorization*"*'
          ),
          strings.ilike(body.html.inner_text, '*"*cancel*"*'),
          strings.ilike(body.html.inner_text, '*"*renew*"*'),
          strings.ilike(body.html.inner_text, '*"*refund*"*'),
          strings.ilike(body.html.inner_text, '*"*+1*"*'),
          regex.icontains(body.html.inner_text, '\"help.{0,3}desk'),
          strings.ilike(body.html.inner_text, '*"* your funds*"*'),
          strings.ilike(body.html.inner_text, '*"* your checking*"*'),
          strings.ilike(body.html.inner_text, '*"* your saving*"*'),
          strings.ilike(body.html.inner_text, '*"*transfer*"*'),
          strings.ilike(body.html.inner_text, '*"*secure your account*"*'),
          strings.ilike(body.html.inner_text, '*"*recover your *"*'),
        )
      )
      or regex.icontains(body.current_thread.text,
                         'note from.{0,50}(?:call|reach|contact|paypal)'
      )
      or any(ml.nlu_classifier(body.current_thread.text).intents,
             .name == "callback_scam"
      )
      or (
        // Unicode confusables words obfuscated in note
        regex.icontains(body.html.inner_text,
                        '\+𝟭|𝗽𝗮𝘆𝗺𝗲𝗻𝘁|𝗛𝗲𝗹𝗽 𝗗𝗲𝘀𝗸|𝗿𝗲𝗳𝘂𝗻𝗱|𝗮𝗻𝘁𝗶𝘃𝗶𝗿𝘂𝘀|𝗰𝗮𝗹𝗹|𝗰𝗮𝗻𝗰𝗲𝗹'
        )
      )
      or strings.ilike(body.html.inner_text, '*"*kindly*"*')
    )
  )
)

Detection logic

Scope: inbound message.

Callback phishing campaigns have been observed abusing Zelle services to send fraudulent payment requests with callback phishing contents.

inbound message
length(attachments) is 0
sender.email.domain.root_domain in ('zellepay.com')
any of:
- body.html.display_text matches '* requested*'
- any of:
  - strings.replace_confusables(subject.subject) matches '.*\\+?([ilo0-9]{1}.)?\\(?[ilo0-9]{3}?\\)?.[ilo0-9]{3}.?[ilo0-9]{4}.*'
  - strings.replace_confusables(subject.subject) matches '.*\\+[ilo0-9]{1,3}[ilo0-9]{10}.*'
  - strings.replace_confusables(subject.subject) matches '.*[ilo0-9]{3}\\.[ilo0-9]{3}\\.[ilo0-9]{4}.*'
  - strings.replace_confusables(subject.subject) matches '.*[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.*'
  - strings.replace_confusables(subject.subject) matches '.*\\([ilo0-9]{3}\\)[\\s-]+[ilo0-9]{3}[\\s-]+[ilo0-9]{4}.*'
  - strings.replace_confusables(subject.subject) matches '.*\\([ilo0-9]{3}\\)-[ilo0-9]{3}-[ilo0-9]{4}.*'
  - all of:
    
    strings.replace_confusables(subject.subject) matches '.*8[ilo0-9]{9}.*'
    strings.replace_confusables(subject.subject) matches '\\+[1li]'
all of:
- any of:
  - strings.replace_confusables(body.current_thread.text) matches '\\".*\\+?([ilo0-9]{1}.)?\\(?[ilo0-9]{3}?\\)?.[ilo0-9]{3}.?[ilo0-9]{4}.*\\"'
  - strings.replace_confusables(body.current_thread.text) matches '\\".*\\+[ilo0-9]{1,3}[ilo0-9]{10}.*\\"'
  - strings.replace_confusables(body.current_thread.text) matches '\\".*[ilo0-9]{3}\\.[ilo0-9]{3}\\.[ilo0-9]{4}.*\\"'
  - strings.replace_confusables(body.current_thread.text) matches '\\".*[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.*\\"'
  - strings.replace_confusables(body.current_thread.text) matches '\\".*\\([ilo0-9]{3}\\)\\s[ilo0-9]{3}-[ilo0-9]{4}.*\\"'
  - strings.replace_confusables(body.current_thread.text) matches '\\".*\\([ilo0-9]{3}\\)-[ilo0-9]{3}-[ilo0-9]{4}.*\\"'
  - all of:
    
    strings.replace_confusables(body.current_thread.text) matches '\\".*8[ilo0-9]{9}.*\\"'
    strings.replace_confusables(body.current_thread.text) matches '\\".*\\+[1li].*\\"'
- any of:
  - at least 4 of 36: body.html.inner_text matches any of 36 patterns
    
    *"*you did not*"*
    *"*is not for*"*
    *"*done by you*"*
    \".*didn\'t ma[kd]e this.*\"
    *"*Fruad Alert*"*
    *"*Fraud Alert*"*
    *"*fraudulent*"*
    *"*Zelle*"*
    *"*subscription*"*
    *"*antivirus*"*
    *"*order*"*
    *"*support*"*
    *"*sincerely apologize*"*
    *"*receipt*"*
    *"*invoice*"*
    *"*Purchase*"*
    *"*transaction*"*
    *"*Market*Value*"*
    *"*BTC*"*
    *"*call*"*
    *"*get in touch with our*"*
    *"*quickly inform*"*
    *"*quickly reach*"*
    *"*detected unusual transactions*
    *"*without your authorization*"*
    *"*cancel*"*
    *"*renew*"*
    *"*refund*"*
    *"*+1*"*
    \"help.{0,3}desk
    *"* your funds*"*
    *"* your checking*"*
    *"* your saving*"*
    *"*transfer*"*
    *"*secure your account*"*
    *"*recover your *"*
  - body.current_thread.text matches 'note from.{0,50}(?:call|reach|contact|paypal)'
  - any of ml.nlu_classifier(body.current_thread.text).intents where:
    
    .name is 'callback_scam'
  - body.html.inner_text matches '\\+𝟭|𝗽𝗮𝘆𝗺𝗲𝗻𝘁|𝗛𝗲𝗹𝗽 𝗗𝗲𝘀𝗸|𝗿𝗲𝗳𝘂𝗻𝗱|𝗮𝗻𝘁𝗶𝘃𝗶𝗿𝘂𝘀|𝗰𝗮𝗹𝗹|𝗰𝗮𝗻𝗰𝗲𝗹'
  - body.html.inner_text matches '*"*kindly*"*'

Inspects: body.current_thread.text, body.html.display_text, body.html.inner_text, sender.email.domain.root_domain, subject.subject, type.inbound. Sensors: ml.nlu_classifier, regex.icontains, strings.ilike, strings.replace_confusables.

Indicators matched (58)

Field	Match	Value
`sender.email.domain.root_domain`	member	`zellepay.com`
`strings.ilike`	substring	`* requested*`
`regex.icontains`	regex	`.\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}.`
`regex.icontains`	regex	`.\+[ilo0-9]{1,3}[ilo0-9]{10}.`
`regex.icontains`	regex	`.[ilo0-9]{3}\.[ilo0-9]{3}\.[ilo0-9]{4}.`
`regex.icontains`	regex	`.[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.`
`regex.icontains`	regex	`.\([ilo0-9]{3}\)[\s-]+[ilo0-9]{3}[\s-]+[ilo0-9]{4}.`
`regex.icontains`	regex	`.\([ilo0-9]{3}\)-[ilo0-9]{3}-[ilo0-9]{4}.`
`regex.icontains`	regex	`.8[ilo0-9]{9}.`
`regex.icontains`	regex	`\+[1li]`
`regex.icontains`	regex	`\".\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}.\"`
`regex.icontains`	regex	`\".\+[ilo0-9]{1,3}[ilo0-9]{10}.\"`

46 more

`regex.icontains`	regex	`\".[ilo0-9]{3}\.[ilo0-9]{3}\.[ilo0-9]{4}.\"`
`regex.icontains`	regex	`\".[ilo0-9]{3}-[ilo0-9]{3}-[ilo0-9]{4}.\"`
`regex.icontains`	regex	`\".\([ilo0-9]{3}\)\s[ilo0-9]{3}-[ilo0-9]{4}.\"`
`regex.icontains`	regex	`\".\([ilo0-9]{3}\)-[ilo0-9]{3}-[ilo0-9]{4}.\"`
`regex.icontains`	regex	`\".8[ilo0-9]{9}.\"`
`regex.icontains`	regex	`\".\+[1li].\"`
`strings.ilike`	substring	`"you did not"`
`strings.ilike`	substring	`"is not for"`
`strings.ilike`	substring	`"done by you"`
`regex.icontains`	regex	`\".didn\'t ma[kd]e this.\"`
`strings.ilike`	substring	`"Fruad Alert"`
`strings.ilike`	substring	`"Fraud Alert"`
`strings.ilike`	substring	`"fraudulent"`
`strings.ilike`	substring	`"Zelle"`
`strings.ilike`	substring	`"subscription"`
`strings.ilike`	substring	`"antivirus"`
`strings.ilike`	substring	`"order"`
`strings.ilike`	substring	`"support"`
`strings.ilike`	substring	`"sincerely apologize"`
`strings.ilike`	substring	`"receipt"`
`strings.ilike`	substring	`"invoice"`
`strings.ilike`	substring	`"Purchase"`
`strings.ilike`	substring	`"transaction"`
`strings.ilike`	substring	`"MarketValue"*`
`strings.ilike`	substring	`"BTC"`
`strings.ilike`	substring	`"call"`
`strings.ilike`	substring	`"get in touch with our"`
`strings.ilike`	substring	`"quickly inform"`
`strings.ilike`	substring	`"quickly reach"`
`strings.ilike`	substring	`"detected unusual transactions*`
`strings.ilike`	substring	`"without your authorization"`
`strings.ilike`	substring	`"cancel"`
`strings.ilike`	substring	`"renew"`
`strings.ilike`	substring	`"refund"`
`strings.ilike`	substring	`"+1"`
`regex.icontains`	regex	`\"help.{0,3}desk`
`strings.ilike`	substring	`" your funds"`
`strings.ilike`	substring	`" your checking"`
`strings.ilike`	substring	`" your saving"`
`strings.ilike`	substring	`"transfer"`
`strings.ilike`	substring	`"secure your account"`
`strings.ilike`	substring	`"recover your "`
`regex.icontains`	regex	`note from.{0,50}(?:call\|reach\|contact\|paypal)`
`ml.nlu_classifier(body.current_thread.text).intents[].name`	equals	`callback_scam`
`regex.icontains`	regex	`\+𝟭\|𝗽𝗮𝘆𝗺𝗲𝗻𝘁\|𝗛𝗲𝗹𝗽 𝗗𝗲𝘀𝗸\|𝗿𝗲𝗳𝘂𝗻𝗱\|𝗮𝗻𝘁𝗶𝘃𝗶𝗿𝘂𝘀\|𝗰𝗮𝗹𝗹\|𝗰𝗮𝗻𝗰𝗲𝗹`
`strings.ilike`	substring	`"kindly"`

`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)