Potential Persistence Via Microsoft Office Startup Folder

Status: test
Severity: high
Log source: product windows, category file_event
Author: Max Altgelt (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects creation of Microsoft Office files inside of one of the default startup folders in order to achieve persistence.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1137` Office Application Startup

Event coverage

Provider	Event	Title
Sysmon	Event ID 11	FileCreate

Rule body yaml

title: Potential Persistence Via Microsoft Office Startup Folder
id: 0e20c89d-2264-44ae-8238-aeeaba609ece
status: test
description: Detects creation of Microsoft Office files inside of one of the default startup folders in order to achieve persistence.
references:
    - https://insight-jp.nttsecurity.com/post/102hojk/operation-restylink-apt-campaign-targeting-japanese-companies
    - https://learn.microsoft.com/en-us/office/troubleshoot/excel/use-startup-folders
author: Max Altgelt (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2022-06-02
modified: 2023-06-22
tags:
    - attack.persistence
    - attack.t1137
logsource:
    category: file_event
    product: windows
detection:
    selection_word_paths:
        - TargetFilename|contains: '\Microsoft\Word\STARTUP'
        - TargetFilename|contains|all:
              - '\Office'
              - '\Program Files'
              - '\STARTUP'
    selection_word_extension:
        TargetFilename|endswith:
            - '.doc'
            - '.docm'
            - '.docx'
            - '.dot'
            - '.dotm'
            - '.rtf'
    selection_excel_paths:
        - TargetFilename|contains: '\Microsoft\Excel\XLSTART'
        - TargetFilename|contains|all:
              - '\Office'
              - '\Program Files'
              - '\XLSTART'
    selection_excel_extension:
        TargetFilename|endswith:
            - '.xls'
            - '.xlsm'
            - '.xlsx'
            - '.xlt'
            - '.xltm'
    filter_main_office:
        Image|endswith:
            - '\WINWORD.exe'
            - '\EXCEL.exe'
    condition: (all of selection_word_* or all of selection_excel_*) and not filter_main_office
falsepositives:
    - Loading a user environment from a backup or a domain controller
    - Synchronization of templates
level: high

Stages and Predicates

Stage 0: `condition`

(all of selection_word_* or all of selection_excel_*) and not filter_main_office

Stage 1: `selection_word_paths`

selection_word_paths:
    - TargetFilename|contains: '\Microsoft\Word\STARTUP'
    - TargetFilename|contains|all:
          - '\Office'
          - '\Program Files'
          - '\STARTUP'

Stage 2: `selection_word_extension`

selection_word_extension:
    TargetFilename|endswith:
        - '.doc'
        - '.docm'
        - '.docx'
        - '.dot'
        - '.dotm'
        - '.rtf'

Stage 3: `selection_excel_paths`

selection_excel_paths:
    - TargetFilename|contains: '\Microsoft\Excel\XLSTART'
    - TargetFilename|contains|all:
          - '\Office'
          - '\Program Files'
          - '\XLSTART'

Stage 4: `selection_excel_extension`

selection_excel_extension:
    TargetFilename|endswith:
        - '.xls'
        - '.xlsm'
        - '.xlsx'
        - '.xlt'
        - '.xltm'

Stage 5: `not filter_main_office`

filter_main_office:
    Image|endswith:
        - '\WINWORD.exe'
        - '\EXCEL.exe'

Exclusions

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

Field	Kind	Excluded values
`Image`	ends_with	`\EXCEL.exe`
`Image`	ends_with	`\WINWORD.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
`TargetFilename`	ends_with	`.doc` `.docm` corpus 4 (sigma 4) `.docx` `.dot` `.dotm` corpus 4 (sigma 4) `.rtf` `.xls` `.xlsm` corpus 4 (sigma 4) `.xlsx` `.xlt` `.xltm` corpus 4 (sigma 4)
`TargetFilename`	match	`\Microsoft\Excel\XLSTART` corpus 2 (sigma 2) `\Microsoft\Word\STARTUP` corpus 2 (sigma 2) `\Office` corpus 2 (sigma 2) `\Program Files` corpus 2 (sigma 2) `\STARTUP` corpus 2 (sigma 2) `\XLSTART` corpus 2 (sigma 2)

`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:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`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)

Potential Persistence Via Microsoft Office Startup Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_word_paths`

Stage 2: `selection_word_extension`

Stage 3: `selection_excel_paths`

Stage 4: `selection_excel_extension`

Stage 5: `not filter_main_office`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Potential Persistence Via Microsoft Office Startup Folder

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_word_paths

Stage 2: selection_word_extension

Stage 3: selection_excel_paths

Stage 4: selection_excel_extension

Stage 5: not filter_main_office

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_word_paths`

Stage 2: `selection_word_extension`

Stage 3: `selection_excel_paths`

Stage 4: `selection_excel_extension`

Stage 5: `not filter_main_office`