External Remote SMB Logon from Public IP

Status: test
Severity: high
Log source: product windows, service security
Author: Micah Babinski (@micahbabinski), Zach Mathis (@yamatosecurity)
Source: github.com/SigmaHQ/sigma

Detects successful logon from public IP address via SMB. This can indicate a publicly-exposed SMB port.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1078` Valid Accounts, `T1133` External Remote Services
Persistence	`T1078` Valid Accounts, `T1133` External Remote Services
Privilege Escalation	`T1078` Valid Accounts
Stealth	`T1078` Valid Accounts
Credential Access	`T1110` Brute Force

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4624	An account was successfully logged on.

Rule body yaml

title: External Remote SMB Logon from Public IP
id: 78d5cab4-557e-454f-9fb9-a222bd0d5edc
related:
    - id: 259a9cdf-c4dd-4fa2-b243-2269e5ab18a2
      type: derived
status: test
description: Detects successful logon from public IP address via SMB. This can indicate a publicly-exposed SMB port.
references:
    - https://www.inversecos.com/2020/04/successful-4624-anonymous-logons-to.html
    - https://twitter.com/Purp1eW0lf/status/1616144561965002752
author: Micah Babinski (@micahbabinski), Zach Mathis (@yamatosecurity)
date: 2023-01-19
modified: 2024-03-11
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.initial-access
    - attack.credential-access
    - attack.stealth
    - attack.t1133
    - attack.t1078
    - attack.t1110
logsource:
    product: windows
    service: security
detection:
    selection:
        EventID: 4624
        LogonType: 3
    filter_main_local_ranges:
        IpAddress|cidr:
            - '::1/128'  # IPv6 loopback
            - '10.0.0.0/8'
            - '127.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '169.254.0.0/16'
            - 'fc00::/7'  # IPv6 private addresses
            - 'fe80::/10'  # IPv6 link-local addresses
    filter_main_empty:
        IpAddress: '-'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Legitimate or intentional inbound connections from public IP addresses on the SMB port.
level: high

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    EventID: 4624
    LogonType: 3

Stage 2: `not filter_main_*`

filter_main_local_ranges:
    IpAddress|cidr:
        - '::1/128'
        - '10.0.0.0/8'
        - '127.0.0.0/8'
        - '172.16.0.0/12'
        - '192.168.0.0/16'
        - '169.254.0.0/16'
        - 'fc00::/7'
        - 'fe80::/10'
filter_main_empty:
    IpAddress: '-'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`IpAddress`	cidr_match	`10.0.0.0/8`
`IpAddress`	cidr_match	`127.0.0.0/8`
`IpAddress`	cidr_match	`169.254.0.0/16`
`IpAddress`	cidr_match	`172.16.0.0/12`
`IpAddress`	cidr_match	`192.168.0.0/16`
`IpAddress`	cidr_match	`::1/128`
`IpAddress`	cidr_match	`fc00::/7`
`IpAddress`	cidr_match	`fe80::/10`
`IpAddress`	eq	`-`

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
`LogonType`	eq	`3` corpus 40 (splunk 13, sigma 12, elastic 9, kusto 6)

`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)

External Remote SMB Logon from Public IP

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

External Remote SMB Logon from Public IP

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`