Bad Opsec Defaults Sacrificial Processes With Improper Arguments

Severity: high
Author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems)
Source: upstream

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
Defense Evasion	`T1218.011` System Binary Proxy Execution: Rundll32

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `1 of selection_werfault`

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

Stage 2: `1 of selection_rundll32`

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

Stage 3: `1 of selection_regsvcs`

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

Stage 4: `1 of selection_regasm`

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

Stage 5: `1 of selection_regsvr32`

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

Stage 6: `not 1 of filter_optional_*`

or:
or:
ParentImage|contains: '\AppData\Local\BraveSoftware\Brave-Browser\Application\'
ParentImage|contains: '\AppData\Local\Google\Chrome\Application\'
CommandLine|endswith: rundll32.exe
Image|endswith: '\rundll32.exe'
ParentCommandLine|contains: '--uninstall '
ParentImage|endswith: '\Installer\setup.exe'
CommandLine|endswith: rundll32.exe
Image|endswith: '\rundll32.exe'
ParentImage|contains: '\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 8 (sigma 8) `\regasm.exe` corpus 4 (sigma 4) `\regsvcs.exe` corpus 3 (sigma 3) `\regsvr32.exe` corpus 57 (sigma 57) `\rundll32.exe` corpus 76 (sigma 76)
`ParentCommandLine`	match	`--uninstall`
`ParentImage`	ends_with	`\Installer\setup.exe`
`ParentImage`	match	`\AppData\Local\BraveSoftware\Brave-Browser\Application\` `\AppData\Local\Google\Chrome\Application\` `\AppData\Local\Microsoft\EdgeUpdate\Install\{`

Bad Opsec Defaults Sacrificial Processes With Improper Arguments

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: 1 of selection_werfault

Stage 2: 1 of selection_rundll32

Stage 3: 1 of selection_regsvcs

Stage 4: 1 of selection_regasm

Stage 5: 1 of selection_regsvr32