Include a virustotal-remove-threat.exe active response script out-of-the-box to delete malicious files in Windows endpoints using VirusTotal events.

[TheMuntu]

Wazuh version	Component	Install type	Install method	Platform
4.4.X	Wazuh agent (active response)	Agent	Packages/Sources	Linux/Unix

Description

This issue aims to have a unified virustotal-remove-threat.exe script that can be used to delete file on Windows endpoints after being flagged as malicious by VirusTotal . This out-of-the-box script will remove the need for users to write their own scripts to remove malicious files which may not be very effective for a wide range of events.

Sample script

This is a sample of a virustotal-remove-threat.py script that can be improved and included out-of-the-box.

#!/usr/bin/python3
# Copyright (C) 2015-2022, Wazuh Inc.
# All rights reserved.

import os
import sys
import json
import datetime

if os.name == 'nt':
    LOG_FILE = "C:\\Program Files (x86)\\ossec-agent\\active-response\\active-responses.log"
else:
    LOG_FILE = "/var/ossec/logs/active-responses.log"

ADD_COMMAND = 0
DELETE_COMMAND = 1
CONTINUE_COMMAND = 2
ABORT_COMMAND = 3

OS_SUCCESS = 0
OS_INVALID = -1

class message:
    def __init__(self):
        self.alert = ""
        self.command = 0

def write_debug_file(ar_name, msg):
    with open(LOG_FILE, mode="a") as log_file:
        log_file.write(str(datetime.datetime.now().strftime('%Y/%m/%d %H:%M:%S')) + " " + ar_name + ": " + msg +"\n")

def setup_and_check_message(argv):

    # get alert from stdin
    input_str = ""
    for line in sys.stdin:
        input_str = line
        break


    try:
        data = json.loads(input_str)
    except ValueError:
        write_debug_file(argv[0], 'Decoding JSON has failed, invalid input format')
        message.command = OS_INVALID
        return message

    message.alert = data

    command = data.get("command")

    if command == "add":
        message.command = ADD_COMMAND
    elif command == "delete":
        message.command = DELETE_COMMAND
    else:
        message.command = OS_INVALID
        write_debug_file(argv[0], 'Not valid command: ' + command)

    return message


def send_keys_and_check_message(argv, keys):

    # build and send message with keys
    keys_msg = json.dumps({"version": 1,"origin":{"name": argv[0],"module":"active-response"},"command":"check_keys","parameters":{"keys":keys}})

    write_debug_file(argv[0], keys_msg)

    print(keys_msg)
    sys.stdout.flush()

    # read the response of previous message
    input_str = ""
    while True:
        line = sys.stdin.readline()
        if line:
            input_str = line
            break

    # write_debug_file(argv[0], input_str)

    try:
        data = json.loads(input_str)
    except ValueError:
        write_debug_file(argv[0], 'Decoding JSON has failed, invalid input format')
        return message

    action = data.get("command")

    if "continue" == action:
        ret = CONTINUE_COMMAND
    elif "abort" == action:
        ret = ABORT_COMMAND
    else:
        ret = OS_INVALID
        write_debug_file(argv[0], "Invalid value of 'command'")

    return ret

def main(argv):

    write_debug_file(argv[0], "Started")

    # validate json and get command
    msg = setup_and_check_message(argv)

    if msg.command < 0:
        sys.exit(OS_INVALID)

    if msg.command == ADD_COMMAND:
        alert = msg.alert["parameters"]["alert"]
        keys = [alert["rule"]["id"]]
        action = send_keys_and_check_message(argv, keys)

        # if necessary, abort execution
        if action != CONTINUE_COMMAND:

            if action == ABORT_COMMAND:
                write_debug_file(argv[0], "Aborted")
                sys.exit(OS_SUCCESS)
            else:
                write_debug_file(argv[0], "Invalid command")
                sys.exit(OS_INVALID)

        try:
            os.remove(msg.alert["parameters"]["alert"]["data"]["virustotal"]["source"]["file"])
            write_debug_file(argv[0], json.dumps(msg.alert) + " Successfully removed threat")
        except OSError as error:
            write_debug_file(argv[0], json.dumps(msg.alert) + "Error removing threat")


    else:
        write_debug_file(argv[0], "Invalid command")

    write_debug_file(argv[0], "Ended")

    sys.exit(OS_SUCCESS)

if __name__ == "__main__":
    main(sys.argv)

Expected configuration

To use this script, add the following configuration to the Wazuh server /var/ossec/etc/ossec.conf file:

<command>
   <name>virustotal-remove-threat</name>
   <executable>virustotal-remove-threat.exe</executable>
   <timeout_allowed>no</timeout_allowed>
</command>

<active-response>
   <disabled>no</disabled>
   <command>virustotal-remove-threat</command>
   <location>local</location>
   <rules_id><USER_DEFINED_RULES_ID></rules_id>
</active-response>

Reference: Using the VirusTotal integration and FIM

Expected execution flow

The steps for the execution of this active response script virustotal-remove-threat.exe will be:

• File integrity monitoring is configured for directories of interest.
• The active response parameters are configured on the Wazuh server to execute the remove threat script when specific rules (rules that indicate that a file has been detected as malware) are triggered.
• A new file is downloaded to the monitored directory on the Windows endpoint.
• This file is detected as malware on VirusTotal.
• The file is removed by the active response script.

Detection alert samples

• File detected as malware using VirusTotal.

{
  "agent": {
    "ip": "172.20.10.7",
    "name": "windows",
    "id": "004"
  },
  "manager": {
    "name": "wazuh-manager"
  },
  "data": {
    "integration": "virustotal",
    "virustotal": {
      "sha1": "3395856ce81f2b7382dee72602f798b642f14140",
      "malicious": "1",
      "total": "68",
      "found": "1",
      "positives": "65",
      "source": {
        "sha1": "3395856ce81f2b7382dee72602f798b642f14140",
        "file": "c:\\programdata\\microsoft\\windows\\start menu\\programs\\startup\\eicar.com.txt",
        "alert_id": "1667312340.22352",
        "md5": "44d88612fea8a8f36de82e1278abb02f"
      },
      "permalink": "https://www.virustotal.com/gui/file/275a021bbfb6489e54d471899f7db9d1663fc695ec2fe2a2c4538aabf651fd0f/detection/f-275a021bbfb6489e54d471899f7db9d1663fc695ec2fe2a2c4538aabf651fd0f-1667311940",
      "scan_date": "2022-11-01 14:12:20"
    }
  },
  "rule": {
    "firedtimes": 1,
    "mail": true,
    "level": 12,
    "pci_dss": [
      "10.6.1",
      "11.4"
    ],
    "description": "VirusTotal: Alert - c:\\programdata\\microsoft\\windows\\start menu\\programs\\startup\\eicar.com.txt - 65 engines detected this file",
    "groups": [
      "virustotal"
    ],
    "mitre": {
      "technique": [
        "Exploitation for Client Execution"
      ],
      "id": [
        "T1203"
      ],
      "tactic": [
        "Execution"
      ]
    },
    "id": "87105",
    "gdpr": [
      "IV_35.7.d"
    ]
  },
  "decoder": {
    "name": "json"
  },
  "input": {
    "type": "log"
  },
  "@timestamp": "2022-11-01T14:19:08.158Z",
  "location": "virustotal",
  "id": "1667312348.23716",
  "timestamp": "2022-11-01T14:19:08.158+0000",
  "_id": "aJWPM4QBB_PjcBLBdTnY"
}

Expected outcome: The file in data.virustotal.source.file is deleted.
Fields of interest: data.virustotal.source.file.
Alert generation guide: [Using the VirusTotal integration and FIM](https://documentation.wazuh.com/current/proof-of-concept-guide/detect-remove-malware-virustotal.html).

General notes

• The script should be able to generate alerts for when the file does not exist, and other possible error cases.
• In addition to creating the script, the documentation should be updated to include instructions and examples for using the active response script.