Potential Defense Evasion Via Binary Rename

Severity: medium
Author: Matthew Green @mgreen27, Ecco, James Pemberton @4A616D6573, oscd.community, Andreas Hunkeler (@Karneades)
Source: upstream

Detects the execution of a renamed binary often used by attackers or malware leveraging new Sysmon OriginalFileName datapoint.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1036.003` Masquerading: Rename Legitimate Utilities

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `selection`

OriginalFileName: [7z.exe, 7za.exe, CONHOST.EXE, Cmd.Exe, InstallUtil.exe, WinRAR.exe, net.exe, net1.exe, netsh.exe, wevtutil.exe]

Stage 2: `not filter`

or:
Image|endswith: '\7z.exe'
Image|endswith: '\7za.exe'
Image|endswith: '\InstallUtil.exe'
Image|endswith: '\WinRAR.exe'
Image|endswith: '\cmd.exe'
Image|endswith: '\conhost.exe'
Image|endswith: '\net.exe'
Image|endswith: '\net1.exe'
Image|endswith: '\netsh.exe'
Image|endswith: '\wevtutil.exe'

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	`\7z.exe` corpus 3 (sigma 3) `\7za.exe` corpus 3 (sigma 3) `\InstallUtil.exe` corpus 5 (sigma 5) `\WinRAR.exe` corpus 2 (sigma 2) `\cmd.exe` corpus 92 (sigma 92) `\conhost.exe` corpus 7 (sigma 7) `\net.exe` corpus 27 (sigma 27) `\net1.exe` corpus 25 (sigma 25) `\netsh.exe` corpus 16 (sigma 16) `\wevtutil.exe` corpus 6 (sigma 6)
`OriginalFileName`	eq	`7z.exe` corpus 3 (sigma 3) `7za.exe` corpus 3 (sigma 3) `CONHOST.EXE` corpus 3 (sigma 3) `Cmd.Exe` corpus 32 (sigma 30, splunk 2) `InstallUtil.exe` corpus 5 (sigma 5) `WinRAR.exe` `net.exe` corpus 16 (sigma 16) `net1.exe` corpus 16 (sigma 16) `netsh.exe` corpus 14 (sigma 14) `wevtutil.exe` corpus 4 (sigma 4)