IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Potential Ransomware Note File Dropped via SMB

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Potential Ransomware Note File Dropped via SMB

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Identifies an incoming SMB connection followed by the creation of a file with a name similar to ransomware note files. This may indicate a remote ransomware attack via the SMB protocol.

Rule type: eql

Rule indices:

logs-endpoint.events.*

Severity: high

Risk score: 73

Runs every: 5m

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

Maximum alerts per execution: 100

References: None

Tags:

Domain: Endpoint
OS: Windows
Use Case: Threat Detection
Tactic: Impact
Resources: Investigation Guide
Data Source: Elastic Defend

Version: 3

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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Triage and analysis

Performance

This rule may cause medium to high performance impact due to logic scoping all icoming SMB network events.

Possible investigation steps

Investigate the source.ip address connecting to port 445 on this host.
Identify the user account that performed the file creation via SMB.
If the number of files is too high and source.ip connecting over SMB is unusual isolate the host and block the used credentials.
Investigate other alerts associated with the user/host during the past 48 hours.

False positive analysis

Remote file creation with similar file naming convention via SMB.

Related rules

Third-party Backup Files Deleted via Unexpected Process - 11ea6bec-ebde-4d71-a8e9-784948f8e3e9
Volume Shadow Copy Deleted or Resized via VssAdmin - b5ea4bfe-a1b2-421f-9d47-22a75a6f2921
Volume Shadow Copy Deletion via PowerShell - d99a037b-c8e2-47a5-97b9-170d076827c4
Volume Shadow Copy Deletion via WMIC - dc9c1f74-dac3-48e3-b47f-eb79db358f57
Suspicious File Renamed via SMB - 78e9b5d5-7c07-40a7-a591-3dbbf464c386

Response and remediation

Initiate the incident response process based on the outcome of the triage.
Consider isolating the involved host to prevent destructive behavior, which is commonly associated with this activity.
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.
If any other destructive action was identified on the host, it is recommended to prioritize the investigation and look for ransomware preparation and execution activities.
If any backups were affected:
Perform data recovery locally or restore the backups from replicated copies (cloud, other servers, etc.).
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 with maxspan=1s
 [network where host.os.type == "windows" and
  event.action == "connection_accepted" and destination.port == 445 and source.port >= 49152 and process.pid == 4 and
  source.ip != "127.0.0.1" and source.ip != "::1" and
  network.type == "ipv4" and not endswith(source.address, destination.address)]
 [file where host.os.type == "windows" and event.action == "creation" and
  process.pid == 4 and user.id : ("S-1-5-21*", "S-1-12-*") and file.extension : ("hta", "txt", "readme", "htm*") and
  file.path : "C:\\Users\\*" and
   /* ransom file name keywords */
    file.name : ("*read*me*", "*lock*", "*@*", "*RECOVER*", "*decrypt*", "*restore*file*", "*FILES_BACK*", "*how*to*")] with runs=3

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Impact
- ID: TA0040
- Reference URL: https://attack.mitre.org/tactics/TA0040/
Technique:
- Name: Data Destruction
- ID: T1485
- Reference URL: https://attack.mitre.org/techniques/T1485/
Technique:
- Name: Inhibit System Recovery
- ID: T1490
- Reference URL: https://attack.mitre.org/techniques/T1490/
Tactic:
- Name: Lateral Movement
- ID: TA0008
- Reference URL: https://attack.mitre.org/tactics/TA0008/
Technique:
- Name: Remote Services
- ID: T1021
- Reference URL: https://attack.mitre.org/techniques/T1021/
Sub-technique:
- Name: SMB/Windows Admin Shares
- ID: T1021.002
- Reference URL: https://attack.mitre.org/techniques/T1021/002/

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