Detection rules › Splunk
Windows Office Product Loaded MSHTML Module
The following analytic detects the loading of the mshtml.dll module into an Office product, which is indicative of CVE-2021-40444 exploitation. It leverages Sysmon EventID 7 to monitor image loads by specific Office processes. This activity is significant because it can indicate an attempt to exploit a vulnerability in the MSHTML component via a malicious document. If confirmed malicious, this could allow an attacker to execute arbitrary code, potentially leading to system compromise, data exfiltration, or further network penetration.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Initial Access | T1566.001 Phishing: Spearphishing Attachment |
Event coverage
| Provider | Event ID | Title |
|---|---|---|
| Sysmon | 7 | Image loaded |
Stages and Predicates
Stage 1: search
search EventID=7 loaded_file_path IN ("*\\IE.Interop.MSHTML.dll", "*\\Microsoft.mshtml.dll", "*\\MshtmlDac.dll", "*\\MshtmlDed.dll", "*\\MshtmlDer.dll", "*\\mshtml.dll") process_name IN ("EQNEDT32.exe", "Graph.exe", "excel.exe", "msaccess.exe", "mspub.exe", "onenote.exe", "onenoteim.exe", "onenotem.exe", "outlook.exe", "powerpnt.exe", "visio.exe", "winproj.exe", "winword.exe", "wordpad.exe", "wordview.exe")
Stage 2: fillnull
fillnull
Stage 3: stats
stats BY Image, ImageLoaded, dest, loaded_file, loaded_file_path, original_file_name, process_exec, process_guid, process_hash, process_id, process_name, process_path, service_dll_signature_exists, service_dll_signature_verified, signature, signature_id, user_id, vendor_product
Stage 4: search
search
Stage 5: search
search
Stage 6: search
search `macro`
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 |
|---|---|---|
EventID | eq |
|
loaded_file_path | in |
|
process_name | in |
|
Neighbors
Broader alternatives (more inclusive than this rule)
These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.
- Windows Remote Access Software BRC4 Loaded Dll (drops 2 filters this rule applies)