Unsigned or Unencrypted SMB Connection to Share Established — Sigma Rule

Rule metadata and linked tags

Author: Mohamed Abdelghani. Source status: experimental; severity: medium. Source dates: 2025-10-19 / not supplied.

{
  "product": "windows",
  "service": "smbserver-connectivity"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: a65cbd65cb098ad020ce3270a0858de0021d1dd6dafc4c62a18ce39287f09324

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Unsigned or Unencrypted SMB Connection to Share Established
id: 8d91f6e4-9f3b-4c21-ae41-2c5b7d9f7a12
status: experimental
description: |
    Detects SMB server connections to shares without signing or encryption enabled.
    This could indicate potential lateral movement activity using unsecured SMB shares.
author: Mohamed Abdelghani
date: 2025-10-19
references:
    - https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/overview-server-message-block-signing
tags:
    - attack.lateral-movement
    - attack.t1021.002
logsource:
    product: windows
    service: smbserver-connectivity
detection:
    selection_shares:
        EventID: 4000
        ShareName|contains:
            - 'IPC$'
            - 'ADMIN$'
            - 'C$'
    selection_status:
        - SigningUsed: 'false'
        - EncyptionUsed: 'false' # Note: typo in the original event field name
    filter_main_local_ips:
        - ClientAddress|cidr:
              # IPv4
              # - '10.0.0.0/8'
              - '127.0.0.0/8'
              - '169.254.0.0/16'
              # - '172.16.0.0/12'
              # - '192.168.0.0/16'
              # IPv6
              - '::1/128'  # IPv6 loopback
              - 'fe80::/10'  # IPv6 link-local addresses
              - 'fc00::/7'  # IPv6 private addresses
        # The filters below cover the XML raw log
        - ClientAddress|contains:
              # IPv6
              - '00000000000000000000000000000001' # ::1 - IPv6 loopback
              - 'FE80000000000000' # fe80:: - IPv6 link-local addresses
              - 'FC00000000000000' # fc00:: - IPv6 private addresses
              # IPv4
              # The "?" are meant to represent the port
              # - '0200????C0A8' # 192.168.
              # - '0200????AC' # 172.
              # - '0200????0A' # 10.
              - '0200????7F' # 127
              - '0200????A9FE' # 169.254.
    condition: all of selection_* and not 1 of filter_main_*
falsepositives:
    - Connections from local or private IP addresses to SMB shares without signing or encryption enabled for older systems or misconfigured environments. Apply additional tuning as needed.
level: medium

Original YAML and metadata in JSON

False positives

• Connections from local or private IP addresses to SMB shares without signing or encryption enabled for older systems or misconfigured environments. Apply additional tuning as needed.

Source references

• https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/overview-server-message-block-signing