Potential Direct Syscall of NtOpenProcess

Status: test
Severity: medium
Log source: product windows, category process_access
Author: Christian Burkard (Nextron Systems), Tim Shelton (FP)
Source: github.com/SigmaHQ/sigma

Detects potential calls to NtOpenProcess directly from NTDLL.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1106` Native API

Event coverage

Provider	Event	Title
Sysmon	Event ID 10	ProcessAccess

Rule body yaml

title: Potential Direct Syscall of NtOpenProcess
id: 3f3f3506-1895-401b-9cc3-e86b16e630d0
status: test
description: Detects potential calls to NtOpenProcess directly from NTDLL.
references:
    - https://medium.com/falconforce/falconfriday-direct-system-calls-and-cobalt-strike-bofs-0xff14-741fa8e1bdd6
author: Christian Burkard (Nextron Systems), Tim Shelton (FP)
date: 2021-07-28
modified: 2023-12-13
tags:
    - attack.execution
    - attack.t1106
logsource:
    category: process_access
    product: windows
detection:
    selection:
        CallTrace|startswith: 'UNKNOWN'
    filter_main_vcredist:
        TargetImage|endswith: 'vcredist_x64.exe'
        SourceImage|endswith: 'vcredist_x64.exe'
    filter_main_generic:
        # Examples include "systeminfo", "backgroundTaskHost", "AUDIODG"
        SourceImage|contains:
            - ':\Program Files (x86)\'
            - ':\Program Files\'
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
            - ':\Windows\WinSxS\'
        TargetImage|contains:
            - ':\Program Files (x86)\'
            - ':\Program Files\'
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
            - ':\Windows\WinSxS\'
    filter_main_kerneltrace_edge:
        # Cases in which the CallTrace is just e.g. 'UNKNOWN(19290435374)' from Microsoft-Windows-Kernel-Audit-API-Calls provider
        Provider_Name: 'Microsoft-Windows-Kernel-Audit-API-Calls'
    filter_optional_vmware:
        TargetImage|endswith: ':\Windows\system32\systeminfo.exe'
        SourceImage|endswith: 'setup64.exe' # vmware
    filter_optional_cylance:
        SourceImage|endswith: ':\Windows\Explorer.EXE'
        TargetImage|endswith: ':\Program Files\Cylance\Desktop\CylanceUI.exe'
    filter_optional_amazon:
        SourceImage|endswith: 'AmazonSSMAgentSetup.exe'
        TargetImage|endswith: 'AmazonSSMAgentSetup.exe'
    filter_optional_vscode: # VsCode
        SourceImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
        TargetImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
    filter_optional_teams: # MS Teams
        TargetImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
        SourceImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
    filter_optional_discord: # Discord
        TargetImage|contains: '\AppData\Local\Discord\'
        TargetImage|endswith: '\Discord.exe'
    filter_optional_yammer:
        SourceImage|contains: '\AppData\Local\yammerdesktop\app-'
        SourceImage|endswith: '\Yammer.exe'
        TargetImage|contains: '\AppData\Local\yammerdesktop\app-'
        TargetImage|endswith: '\Yammer.exe'
        GrantedAccess: '0x1000'
    filter_optional_evernote:
        TargetImage|endswith: '\Evernote\Evernote.exe'
    filter_optional_adobe_acrobat:
        SourceImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
        SourceImage|endswith: '\AcroCEF.exe'
        TargetImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
        TargetImage|endswith: '\AcroCEF.exe'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_* and not 1 of filter_optional_*

Stage 1: `selection`

selection:
    CallTrace|startswith: 'UNKNOWN'

Stage 2: `not filter_main_*`

filter_main_vcredist:
    TargetImage|endswith: 'vcredist_x64.exe'
    SourceImage|endswith: 'vcredist_x64.exe'
filter_main_generic:
    SourceImage|contains:
        - ':\Program Files (x86)\'
        - ':\Program Files\'
        - ':\Windows\System32\'
        - ':\Windows\SysWOW64\'
        - ':\Windows\WinSxS\'
    TargetImage|contains:
        - ':\Program Files (x86)\'
        - ':\Program Files\'
        - ':\Windows\System32\'
        - ':\Windows\SysWOW64\'
        - ':\Windows\WinSxS\'
filter_main_kerneltrace_edge:
    Provider_Name: 'Microsoft-Windows-Kernel-Audit-API-Calls'

Stage 3: `not filter_optional_*`

filter_optional_vmware:
    TargetImage|endswith: ':\Windows\system32\systeminfo.exe'
    SourceImage|endswith: 'setup64.exe'
filter_optional_cylance:
    SourceImage|endswith: ':\Windows\Explorer.EXE'
    TargetImage|endswith: ':\Program Files\Cylance\Desktop\CylanceUI.exe'
filter_optional_amazon:
    SourceImage|endswith: 'AmazonSSMAgentSetup.exe'
    TargetImage|endswith: 'AmazonSSMAgentSetup.exe'
filter_optional_vscode:
    SourceImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
    TargetImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
filter_optional_teams:
    TargetImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
    SourceImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
filter_optional_discord:
    TargetImage|contains: '\AppData\Local\Discord\'
    TargetImage|endswith: '\Discord.exe'
filter_optional_yammer:
    SourceImage|contains: '\AppData\Local\yammerdesktop\app-'
    SourceImage|endswith: '\Yammer.exe'
    TargetImage|contains: '\AppData\Local\yammerdesktop\app-'
    TargetImage|endswith: '\Yammer.exe'
    GrantedAccess: '0x1000'
filter_optional_evernote:
    TargetImage|endswith: '\Evernote\Evernote.exe'
filter_optional_adobe_acrobat:
    SourceImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
    SourceImage|endswith: '\AcroCEF.exe'
    TargetImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
    TargetImage|endswith: '\AcroCEF.exe'

Exclusions

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

Field	Kind	Excluded values
`SourceImage`	match	`:\Program Files (x86)\`
`SourceImage`	match	`:\Program Files\`
`SourceImage`	match	`:\Windows\SysWOW64\`
`SourceImage`	match	`:\Windows\System32\`
`SourceImage`	match	`:\Windows\WinSxS\`
`TargetImage`	match	`:\Program Files (x86)\`
`TargetImage`	match	`:\Program Files\`
`TargetImage`	match	`:\Windows\SysWOW64\`
`TargetImage`	match	`:\Windows\System32\`
`TargetImage`	match	`:\Windows\WinSxS\`
`SourceImage`	ends_with	`vcredist_x64.exe`
`TargetImage`	ends_with	`vcredist_x64.exe`
`Provider_Name`	eq	`Microsoft-Windows-Kernel-Audit-API-Calls`
`GrantedAccess`	eq	`0x1000`
`SourceImage`	ends_with	`\Yammer.exe`
`SourceImage`	match	`\AppData\Local\yammerdesktop\app-`
`TargetImage`	ends_with	`\Yammer.exe`
`TargetImage`	match	`\AppData\Local\yammerdesktop\app-`
`SourceImage`	ends_with	`:\Windows\Explorer.EXE`
`TargetImage`	ends_with	`:\Program Files\Cylance\Desktop\CylanceUI.exe`
`SourceImage`	ends_with	`AmazonSSMAgentSetup.exe`
`TargetImage`	ends_with	`AmazonSSMAgentSetup.exe`
`SourceImage`	ends_with	`\AcroCEF.exe`
`SourceImage`	match	`:\Program Files\Adobe\Acrobat DC\Acrobat\`
`TargetImage`	ends_with	`\AcroCEF.exe`
`TargetImage`	match	`:\Program Files\Adobe\Acrobat DC\Acrobat\`
`SourceImage`	ends_with	`\AppData\Local\Microsoft\Teams\current\Teams.exe`
`TargetImage`	ends_with	`\AppData\Local\Microsoft\Teams\current\Teams.exe`
`SourceImage`	ends_with	`\AppData\Local\Programs\Microsoft VS Code\Code.exe`
`TargetImage`	ends_with	`\AppData\Local\Programs\Microsoft VS Code\Code.exe`
`SourceImage`	ends_with	`setup64.exe`
`TargetImage`	ends_with	`:\Windows\system32\systeminfo.exe`
`TargetImage`	ends_with	`\Discord.exe`
`TargetImage`	match	`\AppData\Local\Discord\`
`TargetImage`	ends_with	`\Evernote\Evernote.exe`

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
`CallTrace`	starts_with	`UNKNOWN`

`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)

Potential Direct Syscall of NtOpenProcess

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Potential Direct Syscall of NtOpenProcess

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Stage 3: not filter_optional_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`