Suspicious Portable Executable Encoded in Powershell Script

  1[metadata]
  2creation_date = "2021/10/15"
  3integration = ["windows"]
  4maturity = "production"
  5updated_date = "2024/10/28"
  6min_stack_version = "8.14.0"
  7min_stack_comments = "Breaking change at 8.14.0 for the Windows Integration."
  8
  9[transform]
 10[[transform.osquery]]
 11label = "Osquery - Retrieve DNS Cache"
 12query = "SELECT * FROM dns_cache"
 13
 14[[transform.osquery]]
 15label = "Osquery - Retrieve All Services"
 16query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 17
 18[[transform.osquery]]
 19label = "Osquery - Retrieve Services Running on User Accounts"
 20query = """
 21SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 22NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 23user_account == null)
 24"""
 25
 26[[transform.osquery]]
 27label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 28query = """
 29SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 30services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 31authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 32"""
 33
 34
 35[rule]
 36author = ["Elastic"]
 37description = """
 38Detects the presence of a portable executable (PE) in a PowerShell script by looking for its encoded header. Attackers
 39embed PEs into PowerShell scripts to inject them into memory, avoiding defences by not writing to disk.
 40"""
 41from = "now-9m"
 42index = ["winlogbeat-*", "logs-windows.powershell*"]
 43language = "kuery"
 44license = "Elastic License v2"
 45name = "Suspicious Portable Executable Encoded in Powershell Script"
 46note = """## Triage and analysis
 47
 48### Investigating Suspicious Portable Executable Encoded in Powershell Script
 49
 50PowerShell is one of the main tools system administrators use for automation, report routines, and other tasks. This makes it available for use in various environments, and creates an attractive way for attackers to execute code.
 51
 52Attackers can abuse PowerShell in-memory capabilities to inject executables into memory without touching the disk, bypassing file-based security protections. These executables are generally base64 encoded.
 53
 54> **Note**:
 55> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/master/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 56
 57#### Possible investigation steps
 58
 59- 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.
 60- 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.
 61- Investigate other alerts associated with the user/host during the past 48 hours.
 62- Evaluate whether the user needs to use PowerShell to complete tasks.
 63- Examine the host for derived artifacts that indicate suspicious activities:
 64  - Analyze the script using a private sandboxed analysis system.
 65  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 66    - Attempts to contact external domains and addresses.
 67      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 68      - Examine the DNS cache for suspicious or anomalous entries.
 69        - $osquery_0
 70    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 71    - Examine the host services for suspicious or anomalous entries.
 72      - $osquery_1
 73      - $osquery_2
 74      - $osquery_3
 75  - Retrieve the files' SHA-256 hash values using the PowerShell `Get-FileHash` cmdlet and search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 76- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 77
 78### False positive analysis
 79
 80- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 81
 82### Related rules
 83
 84- Suspicious .NET Reflection via PowerShell - e26f042e-c590-4e82-8e05-41e81bd822ad
 85- PowerShell Suspicious Payload Encoded and Compressed - 81fe9dc6-a2d7-4192-a2d8-eed98afc766a
 86- PowerShell PSReflect Script - 56f2e9b5-4803-4e44-a0a4-a52dc79d57fe
 87
 88### Response and remediation
 89
 90- Initiate the incident response process based on the outcome of the triage.
 91- Isolate the involved hosts to prevent further post-compromise behavior.
 92- If the triage identified malware, search the environment for additional compromised hosts.
 93  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 94  - Stop suspicious processes.
 95  - Immediately block the identified indicators of compromise (IoCs).
 96  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 97- Remove and block malicious artifacts identified during triage.
 98- Reimage the host operating system or restore the compromised files to clean versions.
 99- Restrict PowerShell usage outside of IT and engineering business units using GPOs, AppLocker, Intune, or similar software.
100- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
101- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
102- 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).
103"""
104references = [
105    "https://github.com/atc-project/atc-data/blob/master/docs/Logging_Policies/LP_0109_windows_powershell_script_block_log.md",
106]
107risk_score = 47
108rule_id = "ad84d445-b1ce-4377-82d9-7c633f28bf9a"
109setup = """## Setup
110
111The 'PowerShell Script Block Logging' logging policy must be enabled.
112Steps to implement the logging policy with Advanced Audit Configuration:

1
2Steps to implement the logging policy via registry:

 1"""
 2severity = "medium"
 3tags = [
 4    "Domain: Endpoint",
 5    "OS: Windows",
 6    "Use Case: Threat Detection",
 7    "Tactic: Execution",
 8    "Tactic: Defense Evasion",
 9    "Resources: Investigation Guide",
10    "Data Source: PowerShell Logs",
11]
12timestamp_override = "event.ingested"
13type = "query"
14
15query = '''
16event.category:process and host.os.type:windows and
17  powershell.file.script_block_text : (
18    TVqQAAMAAAAEAAAA
19  ) and not user.id : "S-1-5-18"
20'''
21
22
23[[rule.threat]]
24framework = "MITRE ATT&CK"
25[[rule.threat.technique]]
26id = "T1059"
27name = "Command and Scripting Interpreter"
28reference = "https://attack.mitre.org/techniques/T1059/"
29[[rule.threat.technique.subtechnique]]
30id = "T1059.001"
31name = "PowerShell"
32reference = "https://attack.mitre.org/techniques/T1059/001/"
33
34
35
36[rule.threat.tactic]
37id = "TA0002"
38name = "Execution"
39reference = "https://attack.mitre.org/tactics/TA0002/"
40[[rule.threat]]
41framework = "MITRE ATT&CK"
42[[rule.threat.technique]]
43id = "T1055"
44name = "Process Injection"
45reference = "https://attack.mitre.org/techniques/T1055/"
46
47
48[rule.threat.tactic]
49id = "TA0005"
50name = "Defense Evasion"
51reference = "https://attack.mitre.org/tactics/TA0005/"