Potential Arbitrary File Download Using Office Application

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems), Beyu Denis, oscd.community
Source: upstream

Detects potential arbitrary file download using a Microsoft Office application

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1202` Indirect Command Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\EXCEL.EXE'
Image|endswith: '\POWERPNT.EXE'
Image|endswith: '\WINWORD.exe'
OriginalFileName: Excel.exe
OriginalFileName: POWERPNT.EXE
OriginalFileName: WinWord.exe

Stage 2: `all of selection_http`

or:
CommandLine|contains: 'http://'
CommandLine|contains: 'https://'

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	`http://` corpus 15 (sigma 15) `https://` corpus 14 (sigma 14)
`Image`	ends_with	`\EXCEL.EXE` corpus 2 (sigma 2) `\POWERPNT.EXE` corpus 4 (sigma 4) `\WINWORD.exe` corpus 5 (sigma 5)
`OriginalFileName`	eq	`Excel.exe` corpus 3 (sigma 3) `POWERPNT.EXE` corpus 3 (sigma 3) `WinWord.exe` corpus 4 (sigma 4)