RDP Brute-force Detection (Windows Event Log)

Group by: _time, host
Source: github.com/anvilogic-forge/armory

Detects possible Brute force attempt over Windows Remote Desktop Protocol (RDP)

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1133` External Remote Services
Persistence	`T1133` External Remote Services
Credential Access	`T1110.001` Brute Force: Password Guessing

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4625	An account failed to log on.
Security-Auditing	Event ID 5156	The Windows Filtering Platform has permitted a connection.

Rule body yaml

id: '5455.5610'
title: RDP Brute-force Detection
description: 'Detects possible Brute force attempt over Windows Remote Desktop Protocol
  (RDP) -- Software Association: BianLian, Conti, LockBit, SamSam, Snatch'
logic_format: Splunk
logic: ' `get_endpoint_data` `get_endpoint_data_winevent` AND ((TERM(EventCode=5156)
  OR "<EventID>5156<") AND Destination_Port="3389" AND Direction="Inbound" AND Protocol="6")
  OR ((TERM(EventCode=4625) OR "<EventID>4625<") AND (Failure_Reason="Unknown user
  name or bad password." OR FailureReason="%%2313" AND Logon_Type="3")) | rex field=Message
  (?<result>"(?i)An account failed to log on.")| rex field=Failure_Reason (?<result_reason>"(?i)Unknown
  user name or bad password.")| eval note=mvappend(result, result_reason)| table _time,
  host, user dest_port, note, process_name, process_path, signature_id, src_country,
  src_dns, src_ip | bin span=20s | stats values(*) as * by _time, host | where match(signature_id,"5156")
  AND match(signature_id,"4625")| where event_count > 3 | lookup dnslookup clientip
  as src_ip OUTPUT clienthost as src_dns | iplocation prefix="src_" src_ip | rename
  src_Country as src_country '
techniques:
- credential-access:brute force:password guessing
- initial-access:external remote services
technique_id:
- T1110.001
- T1133
data_category:
- Windows event logs
references: null

Stages and Predicates

Stage 1: `search`

`get_endpoint_data` `get_endpoint_data_winevent` AND ((TERM(EventCode=5156) OR "<EventID>5156<") AND Destination_Port="3389" AND Direction="Inbound" AND Protocol="6") OR ((TERM(EventCode=4625) OR "<EventID>4625<") AND (Failure_Reason="Unknown user name or bad password." OR FailureReason="%%2313" AND Logon_Type="3"))

Stage 2: `rex`

| rex field=Message (?<result>"(?i)An account failed to log on.")

Stage 3: `rex`

| rex field=Failure_Reason (?<result_reason>"(?i)Unknown user name or bad password.")

Stage 4: `eval`

| eval note=mvappend(result, result_reason)

Stage 5: `table`

| table _time, host, user dest_port, note, process_name, process_path, signature_id, src_country, src_dns, src_ip

Stage 6: `bucket`

| bin span=20s

Stage 7: `stats`

| stats values(*) as * by _time, host

Stage 8: `where`

| where match(signature_id,"5156") AND match(signature_id,"4625")

Stage 9: `where`

| where event_count > 3

Stage 10: `lookup`

| lookup dnslookup clientip as src_ip OUTPUT clienthost as src_dns

Lookup table: dnslookup
Key field: clientip as src_ip
Output columns: ['clienthost', 'src_dns']

Stage 11: `search`

| iplocation prefix="src_" src_ip

Stage 12: `rename`

| rename src_Country as src_country

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Destination_Port`	eq	`"3389"`
`Direction`	eq	`"Inbound"`
`EventCode`	eq	`4625` corpus 15 (splunk 11, chronicle 2, kusto 2) `5156` corpus 15 (splunk 13, kusto 2)
`FailureReason`	eq	`"%%2313"`
`Failure_Reason`	eq	`"Unknown user name or bad password."`
`Logon_Type`	eq	`"3"` corpus 40 (splunk 13, sigma 12, elastic 9, kusto 6)
`Protocol`	eq	`"6"`
`event_count`	gt	`3`
`prefix`	eq	`"src_"` corpus 5 (splunk 5)
`signature_id`	match	`"4625"` `"5156"`

Search terms

Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.

Stage	Term
1	`TERM`
1	`"<EventID>5156<"`
1	`TERM`
1	`"<EventID>4625<"`
11	`iplocation`
11	`src_ip`

`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)

RDP Brute-force Detection (Windows Event Log)

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 1: `search`

Stage 2: `rex`

Stage 3: `rex`

Stage 4: `eval`

Stage 5: `table`

Stage 6: `bucket`

Stage 7: `stats`

Stage 8: `where`

Stage 9: `where`

Stage 10: `lookup`

Stage 11: `search`

Stage 12: `rename`

Indicators

Search terms

Keyboard shortcuts

Search operators

RDP Brute-force Detection (Windows Event Log)

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 1: search

Stage 2: rex

Stage 3: rex

Stage 4: eval

Stage 5: table

Stage 6: bucket

Stage 7: stats

Stage 8: where

Stage 9: where

Stage 10: lookup

Stage 11: search

Stage 12: rename

Indicators

Search terms

Stage 1: `search`

Stage 2: `rex`

Stage 3: `rex`

Stage 4: `eval`

Stage 5: `table`

Stage 6: `bucket`

Stage 7: `stats`

Stage 8: `where`

Stage 9: `where`

Stage 10: `lookup`

Stage 11: `search`

Stage 12: `rename`