Suspicious Spool Service Child Process

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Justin C. (@endisphotic), @dreadphones (detection), Thomas Patzke (Sigma rule)
Source: github.com/SigmaHQ/sigma

Detects suspicious print spool service (spoolsv.exe) child processes.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1203` Exploitation for Client Execution
Privilege Escalation	`T1068` Exploitation for Privilege Escalation

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Suspicious Spool Service Child Process
id: dcdbc940-0bff-46b2-95f3-2d73f848e33b
status: test
description: Detects suspicious print spool service (spoolsv.exe) child processes.
references:
    - https://github.com/microsoft/Microsoft-365-Defender-Hunting-Queries/blob/efa17a600b43c897b4b7463cc8541daa1987eeb4/Exploits/Print%20Spooler%20RCE/Suspicious%20Spoolsv%20Child%20Process.md
author: Justin C. (@endisphotic), @dreadphones (detection), Thomas Patzke (Sigma rule)
date: 2021-07-11
modified: 2024-12-01
tags:
    - attack.execution
    - attack.t1203
    - attack.privilege-escalation
    - attack.t1068
logsource:
    category: process_creation
    product: windows
detection:
    spoolsv:
        ParentImage|endswith: '\spoolsv.exe'
        IntegrityLevel:
            - 'System'
            - 'S-1-16-16384'
    suspicious_unrestricted:
        Image|endswith:
            - '\gpupdate.exe'
            - '\whoami.exe'
            - '\nltest.exe'
            - '\taskkill.exe'
            - '\wmic.exe'
            - '\taskmgr.exe'
            - '\sc.exe'
            - '\findstr.exe'
            - '\curl.exe'
            - '\wget.exe'
            - '\certutil.exe'
            - '\bitsadmin.exe'
            - '\accesschk.exe'
            - '\wevtutil.exe'
            - '\bcdedit.exe'
            - '\fsutil.exe'
            - '\cipher.exe'
            - '\schtasks.exe'
            - '\write.exe'
            - '\wuauclt.exe'
            - '\systeminfo.exe'
            - '\reg.exe'
            - '\query.exe'
    suspicious_net:
        Image|endswith:
            - '\net.exe'
            - '\net1.exe'
    suspicious_net_filter:
        CommandLine|contains: 'start'
    suspicious_cmd:
        Image|endswith: '\cmd.exe'
    suspicious_cmd_filter:
        CommandLine|contains:
            - '.spl'
            - 'route add'
            - 'program files'
    suspicious_netsh:
        Image|endswith: '\netsh.exe'
    suspicious_netsh_filter:
        CommandLine|contains:
            - 'add portopening'
            - 'rule name'
    suspicious_powershell:
        Image|endswith:
            - '\powershell.exe'
            - '\pwsh.exe'
    suspicious_powershell_filter:
        CommandLine|contains: '.spl'
    suspicious_rundll32_img:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: 'RUNDLL32.EXE'
    suspicious_rundll32_cli:
        CommandLine|endswith: 'rundll32.exe'
    condition: spoolsv and ( suspicious_unrestricted or (suspicious_net and not suspicious_net_filter) or (suspicious_cmd and not suspicious_cmd_filter) or (suspicious_netsh and not suspicious_netsh_filter) or (suspicious_powershell and not suspicious_powershell_filter) or all of suspicious_rundll32_* )
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

spoolsv and ( suspicious_unrestricted or (suspicious_net and not suspicious_net_filter) or (suspicious_cmd and not suspicious_cmd_filter) or (suspicious_netsh and not suspicious_netsh_filter) or (suspicious_powershell and not suspicious_powershell_filter) or all of suspicious_rundll32_* )

Stage 1: `spoolsv`

spoolsv:
    ParentImage|endswith: '\spoolsv.exe'
    IntegrityLevel:
        - 'System'
        - 'S-1-16-16384'

Stage 2: `suspicious_unrestricted`

suspicious_unrestricted:
    Image|endswith:
        - '\gpupdate.exe'
        - '\whoami.exe'
        - '\nltest.exe'
        - '\taskkill.exe'
        - '\wmic.exe'
        - '\taskmgr.exe'
        - '\sc.exe'
        - '\findstr.exe'
        - '\curl.exe'
        - '\wget.exe'
        - '\certutil.exe'
        - '\bitsadmin.exe'
        - '\accesschk.exe'
        - '\wevtutil.exe'
        - '\bcdedit.exe'
        - '\fsutil.exe'
        - '\cipher.exe'
        - '\schtasks.exe'
        - '\write.exe'
        - '\wuauclt.exe'
        - '\systeminfo.exe'
        - '\reg.exe'
        - '\query.exe'

Stage 3: `suspicious_net`

suspicious_net:
    Image|endswith:
        - '\net.exe'
        - '\net1.exe'

Stage 4: `not suspicious_net_filter`

suspicious_net_filter:
    CommandLine|contains: 'start'

Stage 5: `suspicious_cmd`

suspicious_cmd:
    Image|endswith: '\cmd.exe'

Stage 6: `not suspicious_cmd_filter`

suspicious_cmd_filter:
    CommandLine|contains:
        - '.spl'
        - 'route add'
        - 'program files'

Stage 7: `suspicious_netsh`

suspicious_netsh:
    Image|endswith: '\netsh.exe'

Stage 8: `not suspicious_netsh_filter`

suspicious_netsh_filter:
    CommandLine|contains:
        - 'add portopening'
        - 'rule name'

Stage 9: `suspicious_powershell`

suspicious_powershell:
    Image|endswith:
        - '\powershell.exe'
        - '\pwsh.exe'

Stage 10: `not suspicious_powershell_filter`

suspicious_powershell_filter:
    CommandLine|contains: '.spl'

Stage 11: `suspicious_rundll32_img`

suspicious_rundll32_img:
    - Image|endswith: '\rundll32.exe'
    - OriginalFileName: 'RUNDLL32.EXE'

Stage 12: `suspicious_rundll32_cli`

suspicious_rundll32_cli:
    CommandLine|endswith: 'rundll32.exe'

Exclusions

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

Field	Kind	Excluded values
`CommandLine`	match	`start`
`CommandLine`	match	`.spl`
`CommandLine`	match	`program files`
`CommandLine`	match	`route add`
`CommandLine`	match	`add portopening`
`CommandLine`	match	`rule name`
`CommandLine`	match	`.spl`

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`	ends_with	`rundll32.exe` corpus 2 (sigma 2)
`Image`	ends_with	`\accesschk.exe` corpus 3 (sigma 3) `\bcdedit.exe` corpus 5 (sigma 5) `\bitsadmin.exe` corpus 29 (sigma 29) `\certutil.exe` corpus 43 (sigma 43) `\cipher.exe` corpus 2 (sigma 2) `\cmd.exe` corpus 130 (sigma 130) `\curl.exe` corpus 30 (sigma 30) `\findstr.exe` corpus 12 (sigma 12) `\fsutil.exe` corpus 5 (sigma 5) `\gpupdate.exe` corpus 2 (sigma 2) `\net.exe` corpus 49 (sigma 49) `\net1.exe` corpus 47 (sigma 47) `\netsh.exe` corpus 28 (sigma 28) `\nltest.exe` corpus 9 (sigma 9) `\powershell.exe` corpus 182 (sigma 182) `\pwsh.exe` corpus 168 (sigma 168) `\query.exe` corpus 6 (sigma 6) `\reg.exe` corpus 58 (sigma 58) `\rundll32.exe` corpus 95 (sigma 95) `\sc.exe` corpus 30 (sigma 30) `\schtasks.exe` corpus 56 (sigma 56) `\systeminfo.exe` corpus 11 (sigma 11) `\taskkill.exe` corpus 4 (sigma 4) `\taskmgr.exe` corpus 5 (sigma 5) `\wevtutil.exe` corpus 9 (sigma 9) `\wget.exe` corpus 9 (sigma 9) `\whoami.exe` corpus 19 (sigma 19) `\wmic.exe` corpus 60 (sigma 60) `\write.exe` `\wuauclt.exe` corpus 3 (sigma 3)
`IntegrityLevel`	eq	`S-1-16-16384` corpus 29 (sigma 22, splunk 4, elastic 3) `System` corpus 29 (sigma 22, splunk 4, elastic 3)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 62 (sigma 35, splunk 21, elastic 6)
`ParentImage`	ends_with	`\spoolsv.exe` corpus 5 (sigma 5)

`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)

Suspicious Spool Service Child Process

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `spoolsv`

Stage 2: `suspicious_unrestricted`

Stage 3: `suspicious_net`

Stage 4: `not suspicious_net_filter`

Stage 5: `suspicious_cmd`

Stage 6: `not suspicious_cmd_filter`

Stage 7: `suspicious_netsh`

Stage 8: `not suspicious_netsh_filter`

Stage 9: `suspicious_powershell`

Stage 10: `not suspicious_powershell_filter`

Stage 11: `suspicious_rundll32_img`

Stage 12: `suspicious_rundll32_cli`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Suspicious Spool Service Child Process

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: spoolsv

Stage 2: suspicious_unrestricted

Stage 3: suspicious_net

Stage 4: not suspicious_net_filter

Stage 5: suspicious_cmd

Stage 6: not suspicious_cmd_filter

Stage 7: suspicious_netsh

Stage 8: not suspicious_netsh_filter

Stage 9: suspicious_powershell

Stage 10: not suspicious_powershell_filter

Stage 11: suspicious_rundll32_img

Stage 12: suspicious_rundll32_cli

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `spoolsv`

Stage 2: `suspicious_unrestricted`

Stage 3: `suspicious_net`

Stage 4: `not suspicious_net_filter`

Stage 5: `suspicious_cmd`

Stage 6: `not suspicious_cmd_filter`

Stage 7: `suspicious_netsh`

Stage 8: `not suspicious_netsh_filter`

Stage 9: `suspicious_powershell`

Stage 10: `not suspicious_powershell_filter`

Stage 11: `suspicious_rundll32_img`

Stage 12: `suspicious_rundll32_cli`