Add-in dropped into a Word or Excel automatic startup folder

Siemphony@siemphonymediumT1137.006unverified

Detects a loadable Office file appearing in one of the two folders whose contents Word and Excel open automatically at launch, which is the file-drop half of AN0137 and the part that survives without any registry write. The two folders are matched as separate arms, each paired with the extensions its own application loads, because a `.dotm` in XLSTART or a `.xlam` in the Word STARTUP folder is inert — a path list AND-ed against one shared extension list would report those crossed pairs as persistence. Excel's arm carries the macro workbook types (`.xlsm`, `.xls`, `.xlsb`, `.xltm`) as well as the add-in types, since XLSTART opens every workbook it contains and runs `Workbook_Open` / `Auto_Open` in it; `PERSONAL.XLSB` is filtered by name rather than by dropping the whole extension, because that one file is what Excel writes when a user records their first macro. `.xll` is included for completeness — Excel is normally pointed at an XLL through the `OPEN=` registry values or the Add-ins manager rather than by finding one in XLSTART. `.ppam` is absent: PowerPoint has no startup folder of this kind and registers add-ins only in the registry, so a `.ppam` written to either matched folder would not load. The user AddIns folder is also excluded, since a file there does nothing until it is registered in the Office Options keys. `\XLSTART\` is matched unanchored because that folder name is distinctive and appears in both the per-user and the Office install-root copies; the Word term is anchored to `\Microsoft\Word\STARTUP\` and therefore covers the per-user folder only, since the install-root equivalent sits under a version-numbered `...\root\OfficeNN\STARTUP\` path that cannot be written without guessing the release. Extensions here populate MITRE's AddInExtension knob; the values are ours. The lock-file filter removes the `~$` shadow files Office itself creates beside an open template. Prerequisite: Sysmon is not present in a default install, and the widely used shipped configurations trim EventID 11 down to a small extension set that does not include `.wll` or `.xlam` — confirm these folders are in scope before reading an empty result as clean. The analytic's other arms — the registry load path and the abnormal Office child process — are separate events and are not modelled here, and this rule cannot show that a dropped file ever loaded. UNVERIFIED AS AUTHORED — derived from MITRE ATT&CK DET0050, not hand-written and not tested by its author. Any lab result is on this rule's own page.Full description

The 4 SIEM queries below are previews produced by Siemphony’s own translator, not pySigma, and none has been executed against a real backend — review before you deploy.

detection.yml

Sentinel · KQL

Run this as a search.

DeviceFileEvents| where ((((FolderPath contains "\\Microsoft\\Word\\STARTUP\\" and (FolderPath endswith ".wll" or FolderPath endswith ".dotm" or FolderPath endswith ".dot")) or (FolderPath contains "\\XLSTART\\" and (FolderPath endswith ".xll" or FolderPath endswith ".xlam" or FolderPath endswith ".xla" or FolderPath endswith ".xlsm" or FolderPath endswith ".xlsb" or FolderPath endswith ".xls" or FolderPath endswith ".xltm"))) and not (FolderPath contains "\\~$")) and not (FolderPath endswith "\\PERSONAL.XLSB"))

Splunk · SPL

Run this as a search.

index=* ((((TargetFilename="*\\Microsoft\\Word\\STARTUP\\*" AND (TargetFilename="*.wll" OR TargetFilename="*.dotm" OR TargetFilename="*.dot")) OR (TargetFilename="*\\XLSTART\\*" AND (TargetFilename="*.xll" OR TargetFilename="*.xlam" OR TargetFilename="*.xla" OR TargetFilename="*.xlsm" OR TargetFilename="*.xlsb" OR TargetFilename="*.xls" OR TargetFilename="*.xltm"))) AND NOT (TargetFilename="*\\~$*")) AND NOT (TargetFilename="*\\PERSONAL.XLSB"))

Elastic · ES|QL

Run this as a search.

FROM logs-*| WHERE ((((TO_LOWER(file.path) LIKE "*\\\\microsoft\\\\word\\\\startup\\\\*" AND (TO_LOWER(file.path) LIKE "*.wll" OR TO_LOWER(file.path) LIKE "*.dotm" OR TO_LOWER(file.path) LIKE "*.dot")) OR (TO_LOWER(file.path) LIKE "*\\\\xlstart\\\\*" AND (TO_LOWER(file.path) LIKE "*.xll" OR TO_LOWER(file.path) LIKE "*.xlam" OR TO_LOWER(file.path) LIKE "*.xla" OR TO_LOWER(file.path) LIKE "*.xlsm" OR TO_LOWER(file.path) LIKE "*.xlsb" OR TO_LOWER(file.path) LIKE "*.xls" OR TO_LOWER(file.path) LIKE "*.xltm"))) AND NOT (TO_LOWER(file.path) LIKE "*\\\\~$*")) AND NOT (TO_LOWER(file.path) LIKE "*\\\\personal.xlsb"))

Wazuh · XML rule

Deploy to your manager — this is a rule, not a search.

<group name="sigma,windows,file_event,">  <!-- Rule ids must be unique on your manager; 100000+ is the user range. -->  <!-- 2 rules: the Sigma condition ORs across different fields,       which one rule cannot express. Any one matching is a hit. -->  <rule id="100000" level="7">    <!-- Set <if_sid> to the decoder/base rule for windows so this only evaluates relevant events. -->    <field name="TargetFilename" type="pcre2">(?i)\\Microsoft\\Word\\STARTUP\\</field>    <field name="TargetFilename" type="pcre2">(?i)(\.wll$|\.dotm$|\.dot$)</field>    <field name="TargetFilename" negate="yes" type="pcre2">(?i)\\~\$</field>    <field name="TargetFilename" negate="yes" type="pcre2">(?i)\\PERSONAL\.XLSB$</field>    <description>Add-in dropped into a Word or Excel automatic startup folder (1/2)</description>    <mitre>      <id>T1137.006</id>    </mitre>  </rule>   <rule id="100001" level="7">    <!-- Set <if_sid> to the decoder/base rule for windows so this only evaluates relevant events. -->    <field name="TargetFilename" type="pcre2">(?i)\\XLSTART\\</field>    <field name="TargetFilename" type="pcre2">(?i)(\.xll$|\.xlam$|\.xla$|\.xlsm$|\.xlsb$|\.xls$|\.xltm$)</field>    <field name="TargetFilename" negate="yes" type="pcre2">(?i)\\~\$</field>    <field name="TargetFilename" negate="yes" type="pcre2">(?i)\\PERSONAL\.XLSB$</field>    <description>Add-in dropped into a Word or Excel automatic startup folder (2/2)</description>    <mitre>      <id>T1137.006</id>    </mitre>  </rule></group>

At a glance

Logsource: file_event / windows
Level: medium
Category: office_macro_execution
Sigma status: experimental
Backends: 4 of 4 rendered
Updated: 30 Aug 2026
Rule ID: 6ec36e84-a40b-4ecc-aa7e-37f64b164579

ATT&CKT1137.006

T1137.006Add-ins

ATT&CK® is a registered trademark of The MITRE Corporation. These mappings are the rule author’s, and are neither reviewed nor endorsed by MITRE.

Lessonoffice macro execution

office macro execution

01 · What this rule detects

A document application — Word, Excel, PowerPoint, Outlook, Publisher, Visio — starting a shell, a script host or a signed proxy binary. The document is the delivery vehicle and the child process is the first thing the attacker actually controls. It is one of the most durable detections available because the parent-child relationship is a property of how the payload has to run, not a string the attacker chooses.

02 · Telemetry you need

Process creation with ParentImage and the full command line — Sysmon EventID 1, or Security 4688 with Audit Process Creation plus the command-line inclusion policy; both off by default, and 4688 without the second one gives you the child process with no arguments
Sysmon EventID 7 (ImageLoad) for the macro runtime — VBE7.DLL and its companions loading into an Office process tells you a macro ran even when nothing was spawned
Sysmon EventID 11 (FileCreate) under %TEMP%, INetCache and the Outlook secure temp folder, where the attachment lands before it is opened
Sysmon EventID 15 (FileCreateStreamHash) for the Mark of the Web zone identifier, which records that the document arrived from outside
Sysmon EventID 3 (NetworkConnect) initiated by the Office process itself

03 · How the logic works

The rule is ParentImage in the Office set AND Image in a child set — shells, script hosts, the signed proxy binaries, and any process launched from a user-writable path. ParentImage carries the signal; the child list is the part you widen over time. The important weakness to teach is that the parent link is breakable: a macro that goes through WMI or a COM object gets its child reparented away from Office, and the rule silently stops matching for exactly the samples that bothered to evade it. That is why the macro-runtime image load and Office writing an executable file are worth having as separate rules rather than as extra conditions on this one — they survive the reparenting. Outlook deserves its own rule too: as a parent it means something different from Word, and the volume profile is different.

04 · Common false positives

Genuine business macros — finance and reporting workbooks that shell out, refresh external data or drive another application
Office add-ins and vendor integrations that launch helper processes, including document management and e-signature tooling
Mail merge, document conversion and reporting pipelines that automate Office on a server
Helpdesk and repair scripts that invoke Office repair or start a shell from a template
Office spawning ordinary Windows infrastructure processes as part of normal operation

05 · Detection maturity

Tier 1 — starting point: Matches an Office application spawning cmd.exe or PowerShell.
Tier 2 — tuned: Covers the full parent set against a broad child set including script hosts and proxy binaries, with named business macros excluded by document path.
Tier 3 — correlated: Adds the macro runtime load and the Mark of the Web, and correlates the chain with what the child process did on the network or wrote to disk.

Tuning & false positivesexperimental · 5 declared

experimental (current stage)
test
stable

Written and reasoned about, but not yet run against real telemetry. Expect to tune it before trusting it.

Tuning tips

Exclude by the document or template path, or by the host running the automation, rather than by the child process — dropping cmd.exe from the child list to quieten one workbook blinds the rule everywhere
Raise severity when the document carries a Mark of the Web zone identifier, and again when it came from Outlook's temp folder
Keep the child list additive, and include 'anything launched from a user-writable directory' as a condition rather than trying to name every binary
Give outlook.exe as parent its own rule so the two can be tuned and prioritised independently
Where the telemetry has it, capture the grandparent as well, so the alert shows the analyst the whole chain rather than one hop

Declared by the author

Add-ins deployed on purpose — a corporate reporting or compliance .xlam pushed by Group Policy or a software-distribution package, or a vendor product that installs a .wll during setup. The rule cannot tell a sanctioned add-in from a dropped one, so these are its main volume, and MITRE's TrustedPath knob is where an estate records the deployment paths and filenames it has approved.
Users installing an add-in themselves from a download or a colleague, which in finance and engineering teams is routine and lands in exactly these folders.
Profile roaming and folder sync. Office repair runs, version upgrades, roaming profiles and OneDrive Known Folder Move all re-materialise the contents of STARTUP and XLSTART, and Known Folder Move in particular produces a burst of creates per user on every first logon to a new machine with no install activity behind it.
Backup, endpoint-protection and search-indexing agents that write a temporary copy of an add-in back into the same folder while scanning or restoring it, producing a file-create event with no user action behind it.
Shared macro workbooks other than PERSONAL.XLSB. Teams that distribute a departmental .xlsm or .xltm into XLSTART so it opens for everyone will match the Excel arm on every deployment and every update.

Noise check0 of 3 fired

Fires on none of the 3 ordinary behaviours the baseline holds for this log type. That is not a precision guarantee: it means only not caught by these 3 behaviours, and the next ordinary behaviour nobody wrote down may still match.

Run live against 65 hand-written events of ordinary corporate activity — backup agents, software distribution, patching, helpdesk scripts, EDR. It says nothing about how often the rule would fire in production, which is the number that actually exhausts an analyst.

Verification1 run

Not verified

Siemphony benign baseline
completed
Siemphony IR · 3 Sept 2026
No events matched, so this run proves nothing either way.

Test it yourselfin your browser

Runs here in your browser against public attack recordings. A preview — not the verification badge.

Recordings of T1137.006, evaluated against their file_event events.

Share this rule

/u/siemphony/6ec36e84-a40b-4ecc-aa7e-37f64b164579

More from this repertoire

All compositions

Verdicts · reactions · comments

Community

Verdicts from engineers who actually deployed it, and the conversation around it.

Not yet reported on

Nobody has run this in a real environment and said what happened.

Verdicts from engineers who deployed it

0 cast

No verdicts reported yet. The first one is worth more than the tenth — say what you ran it against.

No comments yet. Someone who deploys this will have something to say about it.

Add-in dropped into a Word or Excel automatic startup folder

The detection

detection.yml

Sentinel · KQL

Splunk · SPL

Elastic · ES|QL

Wazuh · XML rule

Community

Verdicts from engineers who deployed it