Office Application Initiated Network Connection Over Uncommon Ports

Status: test
Severity: medium
Author: X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

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

Event coverage

Provider	Event	Title
Sysmon	Event ID 3	Network connection

Rule body yaml

title: Office Application Initiated Network Connection Over Uncommon Ports
id: 3b5ba899-9842-4bc2-acc2-12308498bf42
status: test
description: Detects an office suit application (Word, Excel, PowerPoint, Outlook) communicating to target systems over uncommon ports.
references:
    - https://blogs.blackberry.com/en/2023/07/romcom-targets-ukraine-nato-membership-talks-at-nato-summit
author: X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2023-07-12
modified: 2025-10-17
tags:
    - attack.command-and-control
    - attack.stealth
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Initiated: 'true'
        Image|endswith:
            - '\excel.exe'
            - '\outlook.exe'
            - '\powerpnt.exe'
            - '\winword.exe'
            - '\wordview.exe'
    filter_main_common_ports:
        DestinationPort:
            - 53 # DNS
            - 80 # HTTP
            - 139 # NETBIOS
            - 389 # LDAP
            - 443 # HTTPS
            - 445 # SMB
            - 3268 # MSFT-GC
    filter_main_outlook_ports:
        Image|contains: ':\Program Files\Microsoft Office\'
        Image|endswith: '\OUTLOOK.EXE'
        DestinationPort:
            - 143
            - 465 # SMTP
            - 587 # SMTP
            - 993 # IMAP
            - 995 # POP3
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Other ports can be used, apply additional filters accordingly
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

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

Stage 2: `not filter_main_*`

filter_main_common_ports:
    DestinationPort:
        - 53 # DNS
        - 80 # HTTP
        - 139 # NETBIOS
        - 389 # LDAP
        - 443 # HTTPS
        - 445 # SMB
        - 3268 # MSFT-GC
filter_main_outlook_ports:
    Image|contains: ':\Program Files\Microsoft Office\'
    Image|endswith: '\OUTLOOK.EXE'
    DestinationPort:
        - 143
        - 465 # SMTP
        - 587 # SMTP
        - 993 # IMAP
        - 995 # POP3

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Stage	Field	Kind	Excluded values
2	`DestinationPort`	eq	`143`
2	`DestinationPort`	eq	`465`
2	`DestinationPort`	eq	`587`
2	`DestinationPort`	eq	`993`
2	`DestinationPort`	eq	`995`
2	`Image`	ends_with	`\OUTLOOK.EXE`
2	`Image`	match	`:\Program Files\Microsoft Office\`
2	`DestinationPort`	eq	`139`
2	`DestinationPort`	eq	`3268`
2	`DestinationPort`	eq	`389`
2	`DestinationPort`	eq	`443`
2	`DestinationPort`	eq	`445`
2	`DestinationPort`	eq	`53`
2	`DestinationPort`	eq	`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
`Image`	ends_with	`\excel.exe` corpus 24 (sigma 24) `\outlook.exe` corpus 21 (sigma 21) `\powerpnt.exe` corpus 19 (sigma 19) `\winword.exe` corpus 27 (sigma 27) `\wordview.exe` corpus 6 (sigma 6)
`Initiated`	eq	`true` corpus 48 (sigma 48)

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Office Application Initiated Network Connection Over Uncommon Ports

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Office Application Initiated Network Connection Over Uncommon Ports

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`