Regsvr32 Execution From Highly Suspicious Location

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects execution of regsvr32 where the DLL is located in a highly suspicious locations

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.010` System Binary Proxy Execution: Regsvr32

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `selection_img`

or:
Image|endswith: '\regsvr32.exe'
OriginalFileName: REGSVR32.EXE

Stage 2: `selection_path_1`

or:
CommandLine|contains: ':\PerfLogs\'
CommandLine|contains: ':\Temp\'
CommandLine|contains: '\Windows\Registration\CRMLog'
CommandLine|contains: '\Windows\SysWOW64\FxsTmp\'
CommandLine|contains: '\Windows\SysWOW64\Tasks\Microsoft\Windows\PLA\System\'
CommandLine|contains: '\Windows\SysWOW64\Tasks\Microsoft\Windows\SyncCenter\'
CommandLine|contains: '\Windows\SysWOW64\com\dmp\'
CommandLine|contains: '\Windows\System32\FxsTmp\'
CommandLine|contains: '\Windows\System32\Microsoft\Crypto\RSA\MachineKeys\'
CommandLine|contains: '\Windows\System32\Tasks\Microsoft\Windows\SyncCenter\'
CommandLine|contains: '\Windows\System32\Tasks_Migrated\'
CommandLine|contains: '\Windows\System32\com\dmp\'
CommandLine|contains: '\Windows\System32\spool\PRINTERS\'
CommandLine|contains: '\Windows\System32\spool\SERVERS\'
CommandLine|contains: '\Windows\System32\spool\drivers\color\'
CommandLine|contains: '\Windows\Tasks\'
CommandLine|contains: '\Windows\Tracing\'

Stage 3: `selection_path_2`

or:
CommandLine|contains: ' ''C:\'
CommandLine|contains: ' C:\'
CommandLine|contains: ' "C:\'
CommandLine|contains: 'D:\'

Stage 4: `not selection_exclude_known_dirs`

or:
CommandLine|contains: ' ''C:\Windows\'
CommandLine|contains: ' C:\Windows\'
CommandLine|contains: ' "C:\Windows\'
CommandLine|contains: 'C:\Program Files (x86)\'
CommandLine|contains: 'C:\Program Files\'
CommandLine|contains: 'C:\ProgramData\'
CommandLine|contains: 'C:\Users\'

Stage 5: `not 1 of filter_main_*`

or:
CommandLine: ''
CommandLine: null

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	`"C:\` `"C:\Windows\` `'C:\` `'C:\Windows\` `C:\` corpus 2 (sigma 2) `C:\Windows\` corpus 2 (sigma 2) `:\PerfLogs\` corpus 6 (sigma 6) `:\Temp\` corpus 14 (sigma 14) `C:\Program Files (x86)\` `C:\Program Files\` `C:\ProgramData\` corpus 6 (sigma 6) `C:\Users\` corpus 5 (sigma 5) `D:\` `\Windows\Registration\CRMLog` `\Windows\SysWOW64\FxsTmp\` `\Windows\SysWOW64\Tasks\Microsoft\Windows\PLA\System\` `\Windows\SysWOW64\Tasks\Microsoft\Windows\SyncCenter\` `\Windows\SysWOW64\com\dmp\` `\Windows\System32\FxsTmp\` `\Windows\System32\Microsoft\Crypto\RSA\MachineKeys\` `\Windows\System32\Tasks\Microsoft\Windows\SyncCenter\` `\Windows\System32\Tasks_Migrated\` `\Windows\System32\com\dmp\` `\Windows\System32\spool\PRINTERS\` `\Windows\System32\spool\SERVERS\` `\Windows\System32\spool\drivers\color\` `\Windows\Tasks\` `\Windows\Tracing\`
`Image`	ends_with	`\regsvr32.exe` corpus 57 (sigma 57)
`OriginalFileName`	eq	`REGSVR32.EXE` corpus 10 (sigma 10)

Regsvr32 Execution From Highly Suspicious Location

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: selection_img

Stage 2: selection_path_1

Stage 3: selection_path_2