Unsigned or Unencrypted SMB Connection to Share Established

Status: experimental
Severity: medium
Log source: product windows, service smbserver-connectivity
Author: Mohamed Abdelghani
Source: github.com/SigmaHQ/sigma

Detects SMB server connections to shares without signing or encryption enabled. This could indicate potential lateral movement activity using unsecured SMB shares.

MITRE ATT&CK coverage

Tactic	Techniques
Lateral Movement	`T1021.002` Remote Services: SMB/Windows Admin Shares

Event coverage

Provider	Event	Title
SMBServer	Event ID 4000	The SMB client connection to the share was established

Rule body yaml

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

Stages and Predicates

Stage 0: `condition`

all of selection_* and not 1 of filter_main_*

Stage 1: `selection_shares`

selection_shares:
    EventID: 4000
    ShareName|contains:
        - 'IPC$'
        - 'ADMIN$'
        - 'C$'

Stage 2: `selection_status`

selection_status:
    - SigningUsed: 'false'
    - EncyptionUsed: 'false'

Stage 3: `not filter_main_local_ips`

filter_main_local_ips:
    - ClientAddress|cidr:
          - '127.0.0.0/8'
          - '169.254.0.0/16'
          - '::1/128'
          - 'fe80::/10'
          - 'fc00::/7'
    - ClientAddress|contains:
          - '00000000000000000000000000000001'
          - 'FE80000000000000'
          - 'FC00000000000000'
          - '0200????7F'
          - '0200????A9FE'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`ClientAddress`	cidr_match	`127.0.0.0/8`
`ClientAddress`	cidr_match	`169.254.0.0/16`
`ClientAddress`	cidr_match	`::1/128`
`ClientAddress`	cidr_match	`fc00::/7`
`ClientAddress`	cidr_match	`fe80::/10`
`ClientAddress`	match	`00000000000000000000000000000001`
`ClientAddress`	match	`0200????7F`
`ClientAddress`	match	`0200????A9FE`
`ClientAddress`	match	`FC00000000000000`
`ClientAddress`	match	`FE80000000000000`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`EncyptionUsed`	eq	`false`
`ShareName`	match	`ADMIN$` `C$` `IPC$`
`SigningUsed`	eq	`false`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Unsigned or Unencrypted SMB Connection to Share Established

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_shares`

Stage 2: `selection_status`

Stage 3: `not filter_main_local_ips`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Unsigned or Unencrypted SMB Connection to Share Established

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_shares

Stage 2: selection_status

Stage 3: not filter_main_local_ips

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_shares`

Stage 2: `selection_status`

Stage 3: `not filter_main_local_ips`