IMPORTANT: No additional bug fixes or documentation updates
will be released for this version. For the latest information, see the
current release documentation.
Suspicious Portable Executable Encoded in Powershell Script
editSuspicious Portable Executable Encoded in Powershell Script
editDetects the presence of a portable executable (PE) in a PowerShell script by looking for its encoded header. Attackers embed PEs into PowerShell scripts to inject them into memory, avoiding defences by not writing to disk.
Rule type: query
Rule indices:
- winlogbeat-*
- logs-windows.*
Severity: medium
Risk score: 47
Runs every: 5m
Searches indices from: now-9m (Date Math format, see also Additional look-back time
)
Maximum alerts per execution: 100
References:
Tags:
- Elastic
- Host
- Windows
- Threat Detection
- Execution
Version: 9
Rule authors:
- Elastic
Rule license: Elastic License v2
Investigation guide
edit## Triage and analysis ### Investigating Suspicious Portable Executable Encoded in Powershell Script PowerShell 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. Attackers 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. #### 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. - Investigate other alerts associated with the user/host during the past 48 hours. - Evaluate whether the user needs to use PowerShell to complete tasks. - Retrieve the script 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 - This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary. ### Related rules - Suspicious .NET Reflection via PowerShell - e26f042e-c590-4e82-8e05-41e81bd822ad - PowerShell Suspicious Payload Encoded and Compressed - 81fe9dc6-a2d7-4192-a2d8-eed98afc766a - PowerShell PSReflect Script - 56f2e9b5-4803-4e44-a0a4-a52dc79d57fe ### Response and remediation - Initiate the incident response process based on the outcome of the triage. - Isolate the involved hosts 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. - Reimage the host operating system or restore the compromised files to clean versions. - Restrict PowerShell usage outside of IT and engineering business units using GPOs, AppLocker, Intune, or similar software. - 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 enabled. 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 ```
Rule query
editevent.category:process and powershell.file.script_block_text : ( TVqQAAMAAAAEAAAA )
Framework: MITRE ATT&CKTM
-
Tactic:
- Name: Execution
- ID: TA0002
- Reference URL: https://attack.mitre.org/tactics/TA0002/
-
Technique:
- Name: Command and Scripting Interpreter
- ID: T1059
- Reference URL: https://attack.mitre.org/techniques/T1059/
-
Sub-technique:
- Name: PowerShell
- ID: T1059.001
- Reference URL: https://attack.mitre.org/techniques/T1059/001/