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Startup Folder Persistence via Unsigned Process

Elastic Stack Serverless Security

Identifies files written or modified in the startup folder by unsigned processes. Adversaries may abuse this technique to maintain persistence in an environment.

Rule type: eql

Rule indices:

  • logs-endpoint.events.*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Persistence

Version: 100

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

The Windows Startup folder is a special folder in Windows. Programs added to this folder are executed during account
logon, without user interaction, providing an excellent way for attackers to maintain persistence.

This rule looks for unsigned processes writing to the Startup folder locations.

  • Investigate the process 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.
  • Validate the activity is not related to planned patches, updates, network administrator activity, or legitimate
    software installations.
  • Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
  • Retrieve the file 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.
  • There is a high possibility of benign legitimate programs being added to Startup folders. This activity could be based
    on new software installations, patches, or any kind of network administrator related activity. Before entering further
    investigation, verify that this activity is not benign.
  • Suspicious Startup Shell Folder Modification - c8b150f0-0164-475b-a75e-74b47800a9ff
  • Persistent Scripts in the Startup Directory - f7c4dc5a-a58d-491d-9f14-9b66507121c0
  • Initiate the incident response process based on the outcome of the triage.
  • Isolate the involved host 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.
  • Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
    identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
    systems, and web services.
  • 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).

Rule query

sequence by host.id, process.entity_id with maxspan=5s
  [process where event.type in ("start", "process_started") and process.code_signature.trusted == false and
  /* suspicious paths can be added here  */
   process.executable : ("C:\\Users\\*.exe",
                         "C:\\ProgramData\\*.exe",
                         "C:\\Windows\\Temp\\*.exe",
                         "C:\\Windows\\Tasks\\*.exe",
                         "C:\\Intel\\*.exe",
                         "C:\\PerfLogs\\*.exe")
   ]
   [file where event.type != "deletion" and user.domain != "NT AUTHORITY" and
    file.path : ("C:\\Users\\*\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup\\*",
                 "C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\StartUp\\*")
   ]

Framework: MITRE ATT&CKTM