Recon Credential Theft CISA Report

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 * Copyright 2023 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule recon_credential_theft_cisa_report {

  meta:
    author = "Google Cloud Security"
    description = "Detects suspicious credential access commands as identified in CISA Living off the Land pdf. Alone they may be normal but in concert, they may be worth looking into"
    rule_id = "mr_90b80326-d559-4e82-b5da-613e5406127a"
    rule_name = "Recon Credential Theft CISA Report"
    type = "hunt"
    platform = "Windows"
    data_source = "microsoft sysmon"
    tactic = "TA0006"
    technique = "T1555"
    reference = "https://media.defense.gov/2023/May/24/2003229517/-1/-1/0/CSA_Living_off_the_Land.PDF"
    severity = "Low"
    priority = "Low"

  events:
    $process.metadata.event_type = "PROCESS_LAUNCH"
    $process.principal.hostname = $hostname
    $process.target.process.command_line = $command_line

    // cisa report referenced cmd /c in their report throughout, can filter this in/out for tuning as needed
    (
        re.regex($process.target.process.command_line, `(|cmd.*/c).*dir.*C:\\Users\\.*\\.ssh\\known_hosts`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*dir.*C:\\users\\.*\\appdata\\roaming\\Mozilla\\firefox\\profiles`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*mimikatz`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\OpenSSH`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\OpenSSH\\Agent`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\realvnc`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\realvnc\\vncserver`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\realvnc\\Allusers`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hklm\\software\\realvnc\\Allusers\\vncserver`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*query.*hkcu\\software\\.*\\putty\\session`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*save.*hklm\\sam ss.dat`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*reg.*save.*hklm\\system sy.dat`) nocase
    )

  match:
    $hostname over 15m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($process.metadata.id)
    $unique_command_line_threshold = max(5)
    // added to populate alert graph with additional context
    // Commented out principal.hostname because it is already represented in graph as match variable. If match changes, can uncomment to add to results
    //$principal_hostname = array_distinct($process.principal.hostname)
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specific_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specific_process_id = array_distinct($process.target.process.product_specific_process_id)
    $principal_user_userid = array_distinct($process.principal.user.userid)

  condition:
    // modify the condition value for command line to throttle how many of these commands can be issued until the rule is triggered
    $process and #command_line > 5
}