Potential Mpclient.DLL Sideloading Via Defender Binaries

Severity: high
Author: Bhabesh Raj
Source: upstream

Detects potential sideloading of "mpclient.dll" by Windows Defender processes ("MpCmdRun" and "NisSrv") from their non-default directory.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1574.001` Hijack Execution Flow: DLL
Privilege Escalation	`T1574.001` Hijack Execution Flow: DLL
Defense Evasion	`T1574.001` Hijack Execution Flow: DLL

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `selection`

or:
Image|endswith: '\MpCmdRun.exe'
Image|endswith: '\NisSrv.exe'

Stage 2: `not 1 of filter_main_known_locations`

or:
Image|startswith: 'C:\Program Files (x86)\Windows Defender\'
Image|startswith: 'C:\Program Files\Microsoft Security Client\'
Image|startswith: 'C:\Program Files\Windows Defender\'
Image|startswith: 'C:\ProgramData\Microsoft\Windows Defender\Platform\'
Image|startswith: 'C:\Windows\WinSxS\'

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
`Image`	ends_with	`\MpCmdRun.exe` corpus 5 (sigma 5) `\NisSrv.exe` corpus 2 (sigma 2)
`Image`	starts_with	`C:\Program Files (x86)\Windows Defender\` corpus 5 (sigma 5) `C:\Program Files\Microsoft Security Client\` corpus 2 (sigma 2) `C:\Program Files\Windows Defender\` corpus 5 (sigma 5) `C:\ProgramData\Microsoft\Windows Defender\Platform\` corpus 7 (sigma 7) `C:\Windows\WinSxS\` corpus 13 (sigma 13)