Detection: UAC Bypass MMC Load Unsigned Dll

Updated Date: 2024-09-30 ID: 7f04349c-e30d-11eb-bc7f-acde48001122 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the loading of an unsigned DLL by the MMC.exe application, which is indicative of a potential UAC bypass or privilege escalation attempt. It leverages Sysmon EventCode 7 to identify instances where MMC.exe loads a non-Microsoft, unsigned DLL. This activity is significant because attackers often use this technique to modify CLSID registry entries, causing MMC.exe to load malicious DLLs, thereby bypassing User Account Control (UAC) and gaining elevated privileges. If confirmed malicious, this could allow an attacker to execute arbitrary code with higher privileges, leading to further system compromise and persistence.

Search

1`sysmon` EventCode=7  ImageLoaded = "*.dll" Image = "*\\mmc.exe" Signed=false Company != "Microsoft Corporation" 
2| stats count min(_time) as firstTime max(_time) as lastTime by Image ImageLoaded Signed ProcessId OriginalFileName dest EventCode Company 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `uac_bypass_mmc_load_unsigned_dll_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 7	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
uac_bypass_mmc_load_unsigned_dll_filter	`search *`

uac_bypass_mmc_load_unsigned_dll_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1548.002	Bypass User Account Control	Defense Evasion
T1548	Abuse Elevation Control Mechanism	Privilege Escalation
T1218.014	MMC	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT29

APT37

BRONZE BUTLER

Cobalt Group

Earth Lusca

Evilnum

MuddyWater

Patchwork

Threat Group-3390

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To successfully implement this search, you need to be ingesting logs with the process name and imageloaded executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

unknown. all of the dll loaded by mmc.exe is microsoft signed dll.

Associated Analytic Story

Windows Defense Evasion Tactics

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Suspicious unsigned $ImageLoaded$ loaded by $Image$ on endpoint $dest$ with EventCode $EventCode$	63	70	90

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://offsec.almond.consulting/UAC-bypass-dotnet.html

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 3