DLP - PCI: Discover Credit Card Number

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

Detects outbound emails containing Discover credit card numbers in the message body or text-parseable attachments. Discover PANs are 16 digits and start with one of the following BIN ranges: 6011, 622126–622925 (UnionPay co-branded), 644–649, or 65. Optional space or dash separators between digit groups are matched (e.g. 6011 1111 1111 1117 or 6011-1111-1111-1117). Deploy this rule with the "Block Delivery" action to prevent PCI data exfiltration, or in passive mode to monitor and audit outbound mail containing card numbers. Regex engine: RE2 (Golang). No PCRE lookbehind — word boundaries (\b) are used instead. Attachment content is extracted via file.explode() / .scan.strings.strings.

Event coverage

Message attribute
attachments (collection)
body.current_thread
type

Rule body MQL

type.outbound
and (
  // Body: Discover 6011 prefix
  regex.contains(body.current_thread.text,
    '\b6011[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b'
  )

  // Body: Discover 65xx prefix
  or regex.contains(body.current_thread.text,
    '\b65\d{2}[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b'
  )

  // Body: Discover 644–649 prefix
  or regex.contains(body.current_thread.text,
    '\b64[4-9]\d[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b'
  )

  // Body: Discover/UnionPay co-branded 622126–622925
  or regex.contains(body.current_thread.text,
    '\b622(?:1(?:2[6-9]|[3-9]\d)|[2-8]\d{2}|9(?:[01]\d|2[0-5]))\d{2}[\s-]?\d{4}[\s-]?\d{4}\b'
  )

  // Attachments: scan extracted strings from PDFs, Office docs, CSVs, etc.
  or any(attachments,
    .file_extension in~ ('pdf', 'doc', 'docx', 'xls', 'xlsx', 'txt', 'csv', 'eml', 'msg')
    and any(file.explode(.),
      any(.scan.strings.strings,
        regex.contains(., '\b6011[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b')
        or regex.contains(., '\b65\d{2}[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b')
        or regex.contains(., '\b64[4-9]\d[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b')
        or regex.contains(.,
          '\b622(?:1(?:2[6-9]|[3-9]\d)|[2-8]\d{2}|9(?:[01]\d|2[0-5]))\d{2}[\s-]?\d{4}[\s-]?\d{4}\b'
        )
      )
    )
  )
)

Detection logic

Scope: outbound message.

outbound message
any of:
- body.current_thread.text matches '\\b6011[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
- body.current_thread.text matches '\\b65\\d{2}[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
- body.current_thread.text matches '\\b64[4-9]\\d[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
- body.current_thread.text matches '\\b622(?:1(?:2[6-9]|[3-9]\\d)|[2-8]\\d{2}|9(?:[01]\\d|2[0-5]))\\d{2}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
- any of attachments where all hold:
  - .file_extension in ('pdf', 'doc', 'docx', 'xls', 'xlsx', 'txt', 'csv', 'eml', 'msg')
  - any of file.explode(.) where:
    
    any of .scan.strings.strings where any holds:
    
    . matches '\\b6011[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
    . matches '\\b65\\d{2}[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
    . matches '\\b64[4-9]\\d[\\s-]?\\d{4}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'
    . matches '\\b622(?:1(?:2[6-9]|[3-9]\\d)|[2-8]\\d{2}|9(?:[01]\\d|2[0-5]))\\d{2}[\\s-]?\\d{4}[\\s-]?\\d{4}\\b'

Inspects: attachments[].file_extension, body.current_thread.text, type.outbound. Sensors: file.explode, regex.contains.

Indicators matched (13)

Field	Match	Value
`regex.contains`	regex	`\b6011[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b`
`regex.contains`	regex	`\b65\d{2}[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b`
`regex.contains`	regex	`\b64[4-9]\d[\s-]?\d{4}[\s-]?\d{4}[\s-]?\d{4}\b`
`regex.contains`	regex	`\b622(?:1(?:2[6-9]\|[3-9]\d)\|[2-8]\d{2}\|9(?:[01]\d\|2[0-5]))\d{2}[\s-]?\d{4}[\s-]?\d{4}\b`
`attachments[].file_extension`	member	`pdf`
`attachments[].file_extension`	member	`doc`
`attachments[].file_extension`	member	`docx`
`attachments[].file_extension`	member	`xls`
`attachments[].file_extension`	member	`xlsx`
`attachments[].file_extension`	member	`txt`
`attachments[].file_extension`	member	`csv`
`attachments[].file_extension`	member	`eml`

1 more

attachments[].file_extension member msg

`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)

DLP - PCI: Discover Credit Card Number

Event coverage

Rule body MQL

Detection logic

Indicators matched (13)

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