Unusual Executable File Creation by a System Critical Process

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Unusual Executable File Creation by a System Critical Process

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Identifies an unexpected executable file being created or modified by a Windows system critical process, which may indicate activity related to remote code execution or other forms of exploitation.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.*
  • logs-windows.*

Severity: high

Risk score: 73

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Defense Evasion
  • has_guide

Version: 101 (version history)

Added (Elastic Stack release): 7.10.0

Last modified (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

### Investigating Unusual Executable File Creation by a System Critical Process

Windows internal/system processes have some characteristics that can be used to spot suspicious activities. One of these
characteristics is file operations.

This rule looks for the creation of executable files done by system-critical processes. This can indicate the exploitation
of a vulnerability or a malicious process masquerading as a system-critical process.

#### 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.
- Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications,
and any spawned child processes.
- Retrieve the process executable 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 task 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

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

### 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.
- 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).

Rule query

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file where event.type != "deletion" and file.extension : ("exe",
"dll") and process.name : ("smss.exe",
"autochk.exe", "csrss.exe",
"wininit.exe", "services.exe",
"lsass.exe", "winlogon.exe",
"userinit.exe", "LogonUI.exe")

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 101 (8.5.0 release)
  • Formatting only
Version 7 (8.4.0 release)
  • Formatting only
Version 5 (8.2.0 release)
  • Formatting only
Version 4 (7.13.0 release)
  • Updated query, changed from:

    event.category:file and not event.type:deletion and
    file.extension:(exe or dll) and process.name:(smss.exe or autochk.exe
    or csrss.exe or wininit.exe or services.exe or lsass.exe or
    winlogon.exe or userinit.exe or LogonUI.exe)
Version 3 (7.12.0 release)
  • Formatting only
Version 2 (7.11.2 release)
  • Formatting only