VBScript or scriptlet engine loaded into Outlook

Siemphony@siemphonymediumT1137.003unverified

AN0085's process-creation leg — outlook.exe as ParentImage, a script host or staging binary as the child — is not written here. Thirteen of that leg's sixteen child images (powershell, pwsh, cmd, wscript, cscript, mshta, rundll32, regsvr32, certutil, bitsadmin, curl, schtasks, msiexec) and outlook.exe as a parent are already present in this corpus's T1203 rule (data/detections/T1203/rule.yml), so every event the process-creation leg would match also matches T1203, and nothing on either event says which of a malicious form, an Outlook rule (T1137.005), a folder home page (T1137), an opened attachment (T1204.002) or an exploited Outlook (T1203) produced it. That leg is dropped as already covered, in favour of AN0085's other in-brief source: Sysmon EventID 7, where outlook.exe loads vbscript.dll or scrobj.dll to run a form's script. This is at least form-specific in a way the child process never was — a VBA macro loads VBE7.dll instead, not the classic script engine, so this event separates the scripted-form path from the macro path, and it is also earlier in the chain than the eventual child process, catching a form whose script never spawns anything external. Prerequisite, and it is a hard one: since the 2017 Outlook security updates, script in a custom form does not run at all unless HKCU\Software\Microsoft\Office\<version>\Outlook\Security!DisableCustomFormItemScript (a REG_DWORD value, not a subkey) is set to 0 — Ruler-style tooling flips it as part of the attack. On a patched estate with the default left in place, this rule's entire observable never happens and a quiet result reads as "no forms persistence" when the real event was the registry write that enabled it, for which the brief supplies no log source; a companion rule outside this brief would have to carry that signal. Sysmon EventID 7 is itself off in a bare install and, even enabled, commonly restricted to a named DLL allowlist — confirm vbscript.dll and scrobj.dll are in the running configuration before reading an empty result as quiet rather than blind. The remaining two legs of AN0085 are not attempted: the PowerShell form-enumeration script is a separate feed this rule does not read, and MITRE's TimeWindow, OutlookVersion and UserContext knobs describe correlation and baselining lib/sigma cannot express. UNVERIFIED AS AUTHORED — derived from MITRE ATT&CK DET0029, 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.

DeviceImageLoadEvents| where (InitiatingProcessFolderPath endswith "\\outlook.exe" and (FolderPath endswith "\\vbscript.dll" or FolderPath endswith "\\scrobj.dll"))

Splunk · SPL

Run this as a search.

index=* (Image="*\\outlook.exe" AND (ImageLoaded="*\\vbscript.dll" OR ImageLoaded="*\\scrobj.dll"))

Elastic · ES|QL

Run this as a search.

FROM logs-*| WHERE (TO_LOWER(process.executable) LIKE "*\\\\outlook.exe" AND (TO_LOWER(file.path) LIKE "*\\\\vbscript.dll" OR TO_LOWER(file.path) LIKE "*\\\\scrobj.dll"))

Wazuh · XML rule

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

<group name="sigma,windows,image_load,">  <!-- Rule ids must be unique on your manager; 100000+ is the user range. -->  <rule id="100000" level="7">    <!-- Set <if_sid> to the decoder/base rule for windows so this only evaluates relevant events. -->    <field name="Image" type="pcre2">(?i)\\outlook\.exe$</field>    <field name="ImageLoaded" type="pcre2">(?i)(\\vbscript\.dll$|\\scrobj\.dll$)</field>    <description>VBScript or scriptlet engine loaded into Outlook</description>    <mitre>      <id>T1137.003</id>    </mitre>  </rule></group>

At a glance

Logsource: image_load / windows
Level: medium
Category: office_macro_execution
Sigma status: experimental
Backends: 4 of 4 rendered
Updated: 30 Aug 2026
Rule ID: febaae81-6e88-4667-8069-15b86f98bff2

ATT&CKT1137.003

T1137.003Outlook Forms

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 · 4 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

Legitimate custom Outlook forms still deployed on estates that have deliberately set DisableCustomFormItemScript to 0 for an internal workflow — approval routing, helpdesk ticketing or a scripted IPM.Note class built years ago and never retired. On those hosts, and only those hosts, this is the dominant source of matches, which is why the level is not higher.
Previewing or opening a message whose attachment or embedded object is a Windows Script Component (.sct) or another OLE object that the reading pane's preview handler renders, which can load scrobj.dll in-process without any custom form being involved.
Third-party or in-house Outlook add-ins built on the classic Windows Script host rather than VSTO or a modern COM add-in framework, which load vbscript.dll on startup the same way a malicious form's script would.
Endpoint DLP or email-security agents that hook Outlook to inspect message and attachment content for embedded scripts, loading the same script engine into outlook.exe as part of that inspection.

Noise check0 of 2 fired

Fires on none of the 2 ordinary behaviours the baseline holds for this log type. That is not a precision guarantee: it means only not caught by these 2 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 T1137.003, evaluated against their image_load events.

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VBScript or scriptlet engine loaded into Outlook

The detection

detection.yml

Sentinel · KQL

Splunk · SPL

Elastic · ES|QL

Wazuh · XML rule

Community

Verdicts from engineers who deployed it