Publicly Accessible RDP Service

Status: test
Severity: high
Log source: product zeek, service rdp
Author: Josh Brower @DefensiveDepth
Source: github.com/SigmaHQ/sigma

Detects connections from routable IPs to an RDP listener. Which is indicative of a publicly-accessible RDP service.

MITRE ATT&CK coverage

Tactic	Techniques
Lateral Movement	`T1021.001` Remote Services: Remote Desktop Protocol

Rule body yaml

title: Publicly Accessible RDP Service
id: 1fc0809e-06bf-4de3-ad52-25e5263b7623
status: test
description: |
    Detects connections from routable IPs to an RDP listener. Which is indicative of a publicly-accessible RDP service.
author: Josh Brower @DefensiveDepth
date: 2020-08-22
modified: 2024-03-13
tags:
    - attack.lateral-movement
    - attack.t1021.001
logsource:
    product: zeek
    service: rdp
detection:
    selection:
        id.orig_h|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'
            - '2620:83:8000::/48'
            - 'fc00::/7'  # IPv6 private addresses
            - 'fe80::/10'  # IPv6 link-local addresses
    # approved_rdp:
      # dst_ip:
        # - x.x.x.x
    condition: not selection # and not approved_rdp
falsepositives:
    - Although it is recommended to NOT have RDP exposed to the internet, verify that this is a) allowed b) the server has not already been compromised via some brute force or remote exploit since it has been exposed to the internet. Work to secure the server if you are unable to remove it from being exposed to the internet.
level: high

Stages and Predicates

Stage 0: `condition`

not selection # and not approved_rdp

Stage 1: `not selection`

selection:
    id.orig_h|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'
        - '2620:83:8000::/48'
        - 'fc00::/7'
        - 'fe80::/10'

Exclusions

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

Field	Kind	Excluded values
`id.orig_h`	cidr_match	`10.0.0.0/8`
`id.orig_h`	cidr_match	`127.0.0.0/8`
`id.orig_h`	cidr_match	`169.254.0.0/16`
`id.orig_h`	cidr_match	`172.16.0.0/12`
`id.orig_h`	cidr_match	`192.168.0.0/16`
`id.orig_h`	cidr_match	`2620:83:8000::/48`
`id.orig_h`	cidr_match	`::1/128`
`id.orig_h`	cidr_match	`fc00::/7`
`id.orig_h`	cidr_match	`fe80::/10`

`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)

Publicly Accessible RDP Service

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `not selection`

Exclusions

Keyboard shortcuts

Search operators

Publicly Accessible RDP Service

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: not selection

Exclusions

Stage 0: `condition`

Stage 1: `not selection`