Potential Privilege Escalation via InstallerFileTakeOver

## Triage and analysis

### Investigating Potential Privilege Escalation via InstallerFileTakeOver

InstallerFileTakeOver is a weaponized escalation of privilege proof of concept (EoP PoC) to the CVE-2021-41379 vulnerability. Upon successful exploitation, an
unprivileged user will escalate privileges to SYSTEM/NT AUTHORITY.

This rule detects the default execution of the PoC, which overwrites the `elevation_service.exe` DACL and copies itself
to the location to escalate privileges. An attacker is able to still take over any file that is not in use (locked),
which is outside the scope of this rule.

#### Possible investigation steps

- Investigate the process 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.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Look for additional processes spawned by the process, command lines, and network communications.
- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
- Retrieve the file and determine if it is malicious:
  - Use a private sandboxed malware analysis system to perform analysis.
    - Observe and collect information about the following activities:
      - Attempts to contact external domains and addresses.
      - File and registry access, modification, and creation activities.
      - Service creation and launch activities.
      - Scheduled tasks creation.
  - Use the PowerShell Get-FileHash cmdlet to get the files' SHA-256 hash values.
    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.

### False positive analysis

- Verify whether a digital signature exists in the executable, and if it is valid.

### Related rules

- Suspicious DLL Loaded for Persistence or Privilege Escalation - bfeaf89b-a2a7-48a3-817f-e41829dc61ee

### 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.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement temporary network rules, procedures, and segmentation to contain the malware.
  - Stop suspicious processes.
  - Immediately block the identified indicators of compromise (IoCs).
  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
  attackers could use to reinfect the system.
- Remove and block malicious artifacts identified during triage.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- 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.
- 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).