Recon Suspicious Commands CISA Report

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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
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 *     https://www.apache.org/licenses/LICENSE-2.0
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 * 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
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rule recon_suspicious_commands_cisa_report {

  meta:
    author = "Google Cloud Security"
    description = "Detects suspicious 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_66edb4f7-a7e2-4ce6-a247-d09319b7eeea"
    rule_name = "Recon Suspicious Commands CISA Report"
    type = "hunt"
    platform = "Windows"
    data_source = "microsoft sysmon, microsoft windows events"
    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
    // other wmic switches like /user and /password, these have been excluded to focus on the commands being issued since local access does not require these
    (
        re.regex($process.target.process.command_line, `(|cmd.*/c).*7z.*a.*-p.*c:\\windows\\temp\\.*.7z`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*c:\\Windows\\system32\\pcwrun.exe.*c:\\Users\\Administrator\\Desktop\\Win.exe`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c|cmdbak.*/c).*ping.*-n.*1.*127\.0\.0\.1.*c:\\Windows\\temp\\(putty|tmp).log`) nocase or
        // The following line could be swapped for the previous line for a looser match. It was observed during testing that a c2 running powershell logged putty.log as a file creation but not in the command line process event
        //re.regex($process.target.process.command_line, `(|cmd.*/c).*ping.*-n.*1.*127\.0\.0\.1`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*dir.*127\.0\.0\.1\\c\$.*/od`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*ping.*-a.*-n.*1`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*wmic.*process.*call.*create.*net.*stop.*C:\\Windows\\Temp\\tmp.log"`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*\\ADMIN\$\\__.*2>&1`) nocase or
        //The following line could be swapped for the previous line for a looser match, but potentially noisier
        //re.regex($process.target.process.command_line, `(|cmd.*/c).*\\ADMIN\$\\__`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*net.*use.*127\.0\.0\.1\\ipc\$.*/y.*/d`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*powershell.*start-process.*-filepath.*c:\\windows\\temp\\.*.bat.*-windowstyle.*Hidden`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*rar\.exe.*a.*c:\\Windows\\temp\\.*D:\\.*`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*wmic.*cmd.*/c.*whoami`) nocase or
        re.regex($process.target.process.command_line, `(|cmd.*/c).*xcopy.*c:\\windows\\temp\\hp.*d:\\`) nocase
    )

  match:
    $hostname over 15m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($process.metadata.id)
    $unique_command_line_threshold = 5
    // added to populate alert graph with additional context
    // Commented out principal.hostname because it is already represented in graph as match variable. If match changes, can uncomment to add to results
    //$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 unique commands can be seen until the rule is triggered
    $process and #command_line > 5
}