Potential Invoke-Mimikatz PowerShell Script

## Triage and analysis

### Investigating Mimikatz PowerShell Activity

[Mimikatz](https://github.com/gentilkiwi/mimikatz) is an open-source tool used to collect, decrypt, and/or use cached
credentials. This tool is commonly abused by adversaries during the post-compromise stage where adversaries have gained
an initial foothold on an endpoint and are looking to elevate privileges and seek out additional authentication objects
such as tokens/hashes/credentials that can then be used to move laterally and pivot across a network.

This rule looks for PowerShell scripts that load mimikatz in memory, like Invoke-Mimikataz, which are used to dump
credentials from the Local Security Authority Subsystem Service (LSASS). Any activity triggered from this rule should be
treated with high priority as it typically represents an active adversary.

More information about Mimikatz components and how to detect/prevent them can be found on [ADSecurity](https://adsecurity.org/?page_id=1821).

#### Possible investigation steps

- Examine the script content that triggered the detection; look for suspicious DLL imports, collection or exfiltration
capabilities, suspicious functions, encoded or compressed data, and other potentially malicious characteristics.
- Investigate the script execution chain (parent process tree) for unknown processes. Examine their executable files for
prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
- Examine file or network events from the involved PowerShell process for suspicious behavior.
- Investigate other alerts associated with the user/host during the past 48 hours.
  - Invoke-Mimitakz and alike scripts heavily use other capabilities covered by other detections described in the
  "Related Rules" section.
- Evaluate whether the user needs to use PowerShell to complete tasks.
- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the
target host.
  - Examine network and security events in the environment to identify potential lateral movement using compromised credentials.

### False positive analysis

- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.

### Related rules

- PowerShell PSReflect Script - 56f2e9b5-4803-4e44-a0a4-a52dc79d57fe
- Suspicious .NET Reflection via PowerShell - e26f042e-c590-4e82-8e05-41e81bd822ad
- PowerShell Suspicious Payload Encoded and Compressed - 81fe9dc6-a2d7-4192-a2d8-eed98afc766a
- Potential Process Injection via PowerShell - 2e29e96a-b67c-455a-afe4-de6183431d0d
- Mimikatz Memssp Log File Detected - ebb200e8-adf0-43f8-a0bb-4ee5b5d852c6
- Modification of WDigest Security Provider - d703a5af-d5b0-43bd-8ddb-7a5d500b7da5

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
systems, and web services.
- Restrict PowerShell usage outside of IT and engineering business units using GPOs, AppLocker, Intune, or similar software.
- Validate that cleartext passwords are disabled in memory for use with `WDigest`.
- Look into preventing access to `LSASS` using capabilities such as LSA protection or antivirus/EDR tools that provide
this capability.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
mean time to respond (MTTR).

## Setup

The 'PowerShell Script Block Logging' logging policy must be configured (Enable).

Steps to implement the logging policy with with Advanced Audit Configuration:

```
Computer Configuration >
Administrative Templates >
Windows PowerShell >
Turn on PowerShell Script Block Logging (Enable)
```

Steps to implement the logging policy via registry:

```
reg add "hklm\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging" /v EnableScriptBlockLogging /t REG_DWORD /d 1
```