Potentially Suspicious Wuauclt Network Connection

Status: test
Severity: medium
Log source: product windows, category network_connection
Author: Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
Source: github.com/SigmaHQ/sigma

Detects the use of the Windows Update Client binary (wuauclt.exe) to proxy execute code and making network connections. One could easily make the DLL spawn a new process and inject to it to proxy the network connection and bypass this rule.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event	Title
Sysmon	Event ID 3	Network connection

Rule body yaml

title: Potentially Suspicious Wuauclt Network Connection
id: c649a6c7-cd8c-4a78-9c04-000fc76df954
status: test
description: |
    Detects the use of the Windows Update Client binary (wuauclt.exe) to proxy execute code and making network connections.
    One could easily make the DLL spawn a new process and inject to it to proxy the network connection and bypass this rule.
references:
    - https://dtm.uk/wuauclt/
author: Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
date: 2020-10-12
modified: 2024-03-12
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: network_connection
    product: windows
    definition: 'Requirements: The CommandLine field enrichment is required in order for this rule to be used.'
detection:
    selection:
        Image|contains: 'wuauclt'
        CommandLine|contains: ' /RunHandlerComServer'
    # "C:\WINDOWS\uus\AMD64\wuauclt.exe" /DeploymentHandlerFullPath \\?\C:\Windows\UUS\AMD64\UpdateDeploy.dll /ClassId aaa256e1-5b21-4993-9188-18f07ccb3b98 /RunHandlerComServer
    filter_main_ip:
        DestinationIp|cidr: # Ranges excluded based on https://github.com/SigmaHQ/sigma/blob/0f176092326ab9d1e19384d30224e5f29f760d82/rules/windows/network_connection/net_connection_win_dllhost_net_connections.yml
            - '127.0.0.0/8'
            - '10.0.0.0/8'
            - '169.254.0.0/16'  # link-local address
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '::1/128'  # IPv6 loopback
            - 'fe80::/10'  # IPv6 link-local addresses
            - 'fc00::/7'  # IPv6 private addresses
    filter_main_msrange:  # Sysmon
        DestinationIp|cidr:
            - '20.184.0.0/13' # Microsoft Corporation
            - '20.192.0.0/10' # Microsoft Corporation
            - '23.79.0.0/16' # Microsoft Corporation
            - '51.10.0.0/15'
            - '51.103.0.0/16' # Microsoft Corporation
            - '51.104.0.0/15' # Microsoft Corporation
            - '52.224.0.0/11' # Microsoft Corporation
    filter_main_uus:
        CommandLine|contains:
            - ':\Windows\UUS\Packages\Preview\amd64\updatedeploy.dll /ClassId'
            - ':\Windows\UUS\amd64\UpdateDeploy.dll /ClassId'
    filter_main_winsxs:
        CommandLine|contains|all:
            - ':\Windows\WinSxS\'
            - '\UpdateDeploy.dll /ClassId '
    filter_main_cli_null:
        CommandLine: null
    filter_main_cli_empty:
        CommandLine: ''
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    Image|contains: 'wuauclt'
    CommandLine|contains: ' /RunHandlerComServer'

Stage 2: `not filter_main_*`

filter_main_ip:
    DestinationIp|cidr:
        - '127.0.0.0/8'
        - '10.0.0.0/8'
        - '169.254.0.0/16'
        - '172.16.0.0/12'
        - '192.168.0.0/16'
        - '::1/128'
        - 'fe80::/10'
        - 'fc00::/7'
filter_main_msrange:
    DestinationIp|cidr:
        - '20.184.0.0/13'
        - '20.192.0.0/10'
        - '23.79.0.0/16'
        - '51.10.0.0/15'
        - '51.103.0.0/16'
        - '51.104.0.0/15'
        - '52.224.0.0/11'
filter_main_uus:
    CommandLine|contains:
        - ':\Windows\UUS\Packages\Preview\amd64\updatedeploy.dll /ClassId'
        - ':\Windows\UUS\amd64\UpdateDeploy.dll /ClassId'
filter_main_winsxs:
    CommandLine|contains|all:
        - ':\Windows\WinSxS\'
        - '\UpdateDeploy.dll /ClassId '
filter_main_cli_null:
    CommandLine: null
filter_main_cli_empty:
    CommandLine: ''

Exclusions

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

Field	Kind	Excluded values
`CommandLine`	match	`:\Windows\WinSxS\`
`CommandLine`	match	`\UpdateDeploy.dll /ClassId`
`CommandLine`	is_null	(no value, null check)
`CommandLine`	match	`:\Windows\UUS\Packages\Preview\amd64\updatedeploy.dll /ClassId`
`CommandLine`	match	`:\Windows\UUS\amd64\UpdateDeploy.dll /ClassId`
`DestinationIp`	cidr_match	`10.0.0.0/8`
`DestinationIp`	cidr_match	`127.0.0.0/8`
`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	`23.79.0.0/16`
`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
`CommandLine`	match	`/RunHandlerComServer`
`Image`	match	`wuauclt`

`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)

Potentially Suspicious Wuauclt Network Connection

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

Potentially Suspicious Wuauclt Network Connection

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_*`