DllUnregisterServer Function Call Via Msiexec.EXE

Severity: medium
Author: frack113
Source: upstream

Detects MsiExec loading a DLL and calling its DllUnregisterServer function

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.007` System Binary Proxy Execution: Msiexec

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\msiexec.exe'
OriginalFileName: '\msiexec.exe'

Stage 2: `all of selection_flag`

CommandLine|contains: ' -z '

Stage 3: `all of selection_dll`

CommandLine|contains: .dll

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	`-z` `.dll` corpus 15 (sigma 15)
`Image`	ends_with	`\msiexec.exe` corpus 21 (sigma 21)
`OriginalFileName`	eq	`\msiexec.exe` corpus 2 (sigma 2)