Startup Folder Persistence via Unsigned Process

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Startup Folder Persistence via Unsigned Process

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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: 41

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Persistence

Version: 4 (version history)

Added (Elastic Stack release): 7.11.0

Last modified (Elastic Stack release): 8.3.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

### Investigating Startup Folder Persistence via Unsigned Process

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.

#### Possible investigation steps

- 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.

### False positive analysis

- 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.

### Related rules

- Suspicious Startup Shell Folder Modification - c8b150f0-0164-475b-a75e-74b47800a9ff
- Persistent Scripts in the Startup Directory - f7c4dc5a-a58d-491d-9f14-9b66507121c0

### Response and remediation

- 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

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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\\*") ]

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 4 (8.3.0 release)
  • Formatting only
Version 3 (8.2.0 release)
  • Formatting only
Version 2 (7.12.0 release)
  • Formatting only