Office Application Initiated Network Connection Over Uncommon Ports

Severity: medium
Author: X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects an office suit application (Word, Excel, PowerPoint, Outlook) communicating to target systems over uncommon ports.

Event coverage

Provider	Event ID	Title
Sysmon	3	Network connection

Stages and Predicates

Stage 1: `selection`

or:
Image|endswith: '\excel.exe'
Image|endswith: '\outlook.exe'
Image|endswith: '\powerpnt.exe'
Image|endswith: '\winword.exe'
Image|endswith: '\wordview.exe'
Initiated: true

Stage 2: `not 1 of filter_main_*`

or:
DestinationPort: [143, 465, 587, 993, 995]
Image|endswith: '\OUTLOOK.EXE'
Image|contains: ':\Program Files\Microsoft Office\'
DestinationPort: 139
DestinationPort: 3268
DestinationPort: 389
DestinationPort: 443
DestinationPort: 445
DestinationPort: 53
DestinationPort: 80

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
`DestinationPort`	eq	`139` corpus 2 (sigma 2) `143` corpus 2 (sigma 2) `3268` `389` `443` corpus 7 (sigma 7) `445` corpus 3 (sigma 3) `465` corpus 3 (sigma 3) `53` `587` corpus 4 (sigma 4) `80` corpus 6 (sigma 6) `993` corpus 3 (sigma 3) `995` corpus 3 (sigma 3)
`Image`	ends_with	`\OUTLOOK.EXE` corpus 3 (sigma 3) `\excel.exe` corpus 16 (sigma 16) `\outlook.exe` corpus 16 (sigma 16) `\powerpnt.exe` corpus 13 (sigma 13) `\winword.exe` corpus 17 (sigma 17) `\wordview.exe` corpus 6 (sigma 6)
`Image`	match	`:\Program Files\Microsoft Office\` corpus 4 (sigma 4)
`Initiated`	eq	`true` corpus 40 (sigma 40)