Bad Opsec Defaults Sacrificial Processes With Improper Arguments

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects attackers using tooling with bad opsec defaults. E.g. spawning a sacrificial process to inject a capability into the process without taking into account how the process is normally run. One trivial example of this is using rundll32.exe without arguments as a sacrificial process (default in CS, now highlighted by c2lint), running WerFault without arguments (Kraken - credit am0nsec), and other examples.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218.011` System Binary Proxy Execution: Rundll32

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Bad Opsec Defaults Sacrificial Processes With Improper Arguments
id: a7c3d773-caef-227e-a7e7-c2f13c622329
related:
    - id: f5647edc-a7bf-4737-ab50-ef8c60dc3add
      type: obsolete
status: test
description: |
    Detects attackers using tooling with bad opsec defaults.
    E.g. spawning a sacrificial process to inject a capability into the process without taking into account how the process is normally run.
    One trivial example of this is using rundll32.exe without arguments as a sacrificial process (default in CS, now highlighted by c2lint), running WerFault without arguments (Kraken - credit am0nsec), and other examples.
references:
    - https://blog.malwarebytes.com/malwarebytes-news/2020/10/kraken-attack-abuses-wer-service/
    - https://www.cobaltstrike.com/help-opsec
    - https://twitter.com/CyberRaiju/status/1251492025678983169
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/regsvr32
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/rundll32
    - https://learn.microsoft.com/en-us/dotnet/framework/tools/regasm-exe-assembly-registration-tool
    - https://learn.microsoft.com/en-us/dotnet/framework/tools/regsvcs-exe-net-services-installation-tool
author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems)
date: 2020-10-23
modified: 2024-08-15
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection_werfault:
        Image|endswith: '\WerFault.exe'
        CommandLine|endswith: 'WerFault.exe'
    selection_rundll32:
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    selection_regsvcs:
        Image|endswith: '\regsvcs.exe'
        CommandLine|endswith: 'regsvcs.exe'
    selection_regasm:
        Image|endswith: '\regasm.exe'
        CommandLine|endswith: 'regasm.exe'
    selection_regsvr32:
        Image|endswith: '\regsvr32.exe'
        CommandLine|endswith: 'regsvr32.exe'
    filter_optional_edge_update:
        ParentImage|contains: '\AppData\Local\Microsoft\EdgeUpdate\Install\{'
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    filter_optional_chromium_installer:
        # As reported in https://github.com/SigmaHQ/sigma/issues/4570 and others
        ParentImage|contains:
            - '\AppData\Local\BraveSoftware\Brave-Browser\Application\'
            - '\AppData\Local\Google\Chrome\Application\'
        ParentImage|endswith: '\Installer\setup.exe'
        ParentCommandLine|contains: '--uninstall '
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    condition: 1 of selection_* and not 1 of filter_optional_*
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

1 of selection_* and not 1 of filter_optional_*

Stage 1: `selection_werfault`

selection_werfault:
    Image|endswith: '\WerFault.exe'
    CommandLine|endswith: 'WerFault.exe'

Stage 2: `selection_rundll32`

selection_rundll32:
    Image|endswith: '\rundll32.exe'
    CommandLine|endswith: 'rundll32.exe'

Stage 3: `selection_regsvcs`

selection_regsvcs:
    Image|endswith: '\regsvcs.exe'
    CommandLine|endswith: 'regsvcs.exe'

Stage 4: `selection_regasm`

selection_regasm:
    Image|endswith: '\regasm.exe'
    CommandLine|endswith: 'regasm.exe'

Stage 5: `selection_regsvr32`

selection_regsvr32:
    Image|endswith: '\regsvr32.exe'
    CommandLine|endswith: 'regsvr32.exe'

Stage 6: `not filter_optional_*`

filter_optional_edge_update:
    ParentImage|contains: '\AppData\Local\Microsoft\EdgeUpdate\Install\{'
    Image|endswith: '\rundll32.exe'
    CommandLine|endswith: 'rundll32.exe'
filter_optional_chromium_installer:
    ParentImage|contains:
        - '\AppData\Local\BraveSoftware\Brave-Browser\Application\'
        - '\AppData\Local\Google\Chrome\Application\'
    ParentImage|endswith: '\Installer\setup.exe'
    ParentCommandLine|contains: '--uninstall '
    Image|endswith: '\rundll32.exe'
    CommandLine|endswith: 'rundll32.exe'

Exclusions

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

Field	Kind	Excluded values
`ParentImage`	match	`\AppData\Local\BraveSoftware\Brave-Browser\Application\`
`ParentImage`	match	`\AppData\Local\Google\Chrome\Application\`
`CommandLine`	ends_with	`rundll32.exe`
`Image`	ends_with	`\rundll32.exe`
`ParentCommandLine`	match	`--uninstall`
`ParentImage`	ends_with	`\Installer\setup.exe`
`CommandLine`	ends_with	`rundll32.exe`
`Image`	ends_with	`\rundll32.exe`
`ParentImage`	match	`\AppData\Local\Microsoft\EdgeUpdate\Install\{`

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	`WerFault.exe` `regasm.exe` `regsvcs.exe` `regsvr32.exe` `rundll32.exe` corpus 2 (sigma 2)
`Image`	ends_with	`\WerFault.exe` corpus 9 (sigma 9) `\regasm.exe` corpus 9 (sigma 9) `\regsvcs.exe` corpus 8 (sigma 8) `\regsvr32.exe` corpus 65 (sigma 65) `\rundll32.exe` corpus 95 (sigma 95)

`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)

Bad Opsec Defaults Sacrificial Processes With Improper Arguments

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_werfault`

Stage 2: `selection_rundll32`

Stage 3: `selection_regsvcs`

Stage 4: `selection_regasm`

Stage 5: `selection_regsvr32`

Stage 6: `not filter_optional_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Bad Opsec Defaults Sacrificial Processes With Improper Arguments

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_werfault

Stage 2: selection_rundll32

Stage 3: selection_regsvcs

Stage 4: selection_regasm

Stage 5: selection_regsvr32

Stage 6: not filter_optional_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_werfault`

Stage 2: `selection_rundll32`

Stage 3: `selection_regsvcs`

Stage 4: `selection_regasm`

Stage 5: `selection_regsvr32`

Stage 6: `not filter_optional_*`