Dllhost.EXE Initiated Network Connection To Non-Local IP Address

Status: test
Severity: medium
Log source: product windows, category network_connection
Author: bartblaze
Source: github.com/SigmaHQ/sigma

Detects Dllhost.EXE initiating a network connection to a non-local IP address. Aside from Microsoft own IP range that needs to be excluded. Network communication from Dllhost will depend entirely on the hosted DLL. An initial baseline is recommended before deployment.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1559.001` Inter-Process Communication: Component Object Model
Stealth	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event	Title
Sysmon	Event ID 3	Network connection

Rule body yaml

title: Dllhost.EXE Initiated Network Connection To Non-Local IP Address
id: cfed2f44-16df-4bf3-833a-79405198b277
status: test
description: |
    Detects Dllhost.EXE initiating a network connection to a non-local IP address.
    Aside from Microsoft own IP range that needs to be excluded. Network communication from Dllhost will depend entirely on the hosted DLL.
    An initial baseline is recommended before deployment.
references:
    - https://redcanary.com/blog/child-processes/
    - https://nasbench.medium.com/what-is-the-dllhost-exe-process-actually-running-ef9fe4c19c08
author: bartblaze
date: 2020-07-13
modified: 2024-07-16
tags:
    - attack.stealth
    - attack.t1218
    - attack.execution
    - attack.t1559.001
    - detection.threat-hunting
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Image|endswith: '\dllhost.exe'
        Initiated: 'true'
    filter_main_local_ranges:
        DestinationIp|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_msrange:
        DestinationIp|cidr:
            - '20.184.0.0/13' # Microsoft Corporation
            - '20.192.0.0/10' # Microsoft Corporation
            - '23.72.0.0/13'  # Akamai International B.V.
            - '51.10.0.0/15'  # Microsoft Corporation
            - '51.103.0.0/16' # Microsoft Corporation
            - '51.104.0.0/15' # Microsoft Corporation
            - '52.224.0.0/11'  # Microsoft Corporation
            - '150.171.0.0/19'  # Microsoft Corporation
            - '204.79.197.0/24' # Microsoft Corporation'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Communication to other corporate systems that use IP addresses from public address spaces
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    Image|endswith: '\dllhost.exe'
    Initiated: 'true'

Stage 2: `not filter_main_*`

filter_main_local_ranges:
    DestinationIp|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_msrange:
    DestinationIp|cidr:
        - '20.184.0.0/13'
        - '20.192.0.0/10'
        - '23.72.0.0/13'
        - '51.10.0.0/15'
        - '51.103.0.0/16'
        - '51.104.0.0/15'
        - '52.224.0.0/11'
        - '150.171.0.0/19'
        - '204.79.197.0/24'

Exclusions

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

Field	Kind	Excluded values
`DestinationIp`	cidr_match	`10.0.0.0/8`
`DestinationIp`	cidr_match	`127.0.0.0/8`
`DestinationIp`	cidr_match	`150.171.0.0/19`
`DestinationIp`	cidr_match	`169.254.0.0/16`
`DestinationIp`	cidr_match	`172.16.0.0/12`
`DestinationIp`	cidr_match	`192.168.0.0/16`
`DestinationIp`	cidr_match	`20.184.0.0/13`
`DestinationIp`	cidr_match	`20.192.0.0/10`
`DestinationIp`	cidr_match	`204.79.197.0/24`
`DestinationIp`	cidr_match	`23.72.0.0/13`
`DestinationIp`	cidr_match	`51.10.0.0/15`
`DestinationIp`	cidr_match	`51.103.0.0/16`
`DestinationIp`	cidr_match	`51.104.0.0/15`
`DestinationIp`	cidr_match	`52.224.0.0/11`
`DestinationIp`	cidr_match	`::1/128`
`DestinationIp`	cidr_match	`fc00::/7`
`DestinationIp`	cidr_match	`fe80::/10`

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
`Image`	ends_with	`\dllhost.exe` corpus 11 (sigma 11)
`Initiated`	eq	`true` corpus 50 (sigma 50)

`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)

Dllhost.EXE Initiated Network Connection To Non-Local IP Address

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

Dllhost.EXE Initiated Network Connection To Non-Local IP Address

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_*`