NetNTLM Downgrade Attack - Registry

Status: test
Severity: high
Log source: product windows, category registry_event
Author: Florian Roth (Nextron Systems), wagga, Nasreddine Bencherchali (Splunk STRT)
Source: github.com/SigmaHQ/sigma

Detects NetNTLM downgrade attack

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1112` Modify Registry
Defense Impairment	`T1112` Modify Registry, `T1685` Disable or Modify Tools

Event coverage

Provider	Event	Title
Sysmon	Event ID 12	RegistryEvent (Object create and delete)
Sysmon	Event ID 13	RegistryEvent (Value Set)
Sysmon	Event ID 14	RegistryEvent (Key and Value Rename)

Rule body yaml

title: NetNTLM Downgrade Attack - Registry
id: d67572a0-e2ec-45d6-b8db-c100d14b8ef2
status: test
description: Detects NetNTLM downgrade attack
references:
    - https://web.archive.org/web/20171113231705/https://www.optiv.com/blog/post-exploitation-using-netntlm-downgrade-attacks
    - https://www.ultimatewindowssecurity.com/wiki/page.aspx?spid=NSrpcservers
author: Florian Roth (Nextron Systems), wagga, Nasreddine Bencherchali (Splunk STRT)
date: 2018-03-20
modified: 2024-12-03
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1685
    - attack.t1112
logsource:
    product: windows
    category: registry_event
detection:
    selection_regkey:
        TargetObject|contains|all:
            - 'SYSTEM\'
            - 'ControlSet'
            - '\Control\Lsa'
    selection_value_lmcompatibilitylevel:
        TargetObject|endswith: '\lmcompatibilitylevel'
        Details:
            - 'DWORD (0x00000000)'
            - 'DWORD (0x00000001)'
            - 'DWORD (0x00000002)'
    selection_value_ntlmminclientsec:
        TargetObject|endswith: '\NtlmMinClientSec'
        Details:
            - 'DWORD (0x00000000)' # No Security
            - 'DWORD (0x00000010)' # Only Integrity
            - 'DWORD (0x00000020)' # Only confidentiality
            - 'DWORD (0x00000030)' # Both Integrity and confidentiality
    selection_value_restrictsendingntlmtraffic:
        # Note: The obvious values with issues are 0x00000000 (allow all) and 0x00000001 (audit).
        # 0x00000002 can be secure but only if "ClientAllowedNTLMServers" is properly configured
        # Hence all values should be monitored and investigated
        TargetObject|endswith: '\RestrictSendingNTLMTraffic'
    condition: selection_regkey and 1 of selection_value_*
falsepositives:
    - Services or tools that set the values to more restrictive values
level: high

Stages and Predicates

Stage 0: `condition`

selection_regkey and 1 of selection_value_*

Stage 1: `selection_regkey`

selection_regkey:
    TargetObject|contains|all:
        - 'SYSTEM\'
        - 'ControlSet'
        - '\Control\Lsa'

Stage 2: `selection_value_lmcompatibilitylevel`

selection_value_lmcompatibilitylevel:
    TargetObject|endswith: '\lmcompatibilitylevel'
    Details:
        - 'DWORD (0x00000000)'
        - 'DWORD (0x00000001)'
        - 'DWORD (0x00000002)'

Stage 3: `selection_value_ntlmminclientsec`

selection_value_ntlmminclientsec:
    TargetObject|endswith: '\NtlmMinClientSec'
    Details:
        - 'DWORD (0x00000000)'
        - 'DWORD (0x00000010)'
        - 'DWORD (0x00000020)'
        - 'DWORD (0x00000030)'

Stage 4: `selection_value_restrictsendingntlmtraffic`

selection_value_restrictsendingntlmtraffic:
    TargetObject|endswith: '\RestrictSendingNTLMTraffic'

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
`Details`	eq	`DWORD (0x00000000)` corpus 38 (sigma 36, chronicle 2) `DWORD (0x00000001)` corpus 40 (sigma 36, chronicle 4) `DWORD (0x00000002)` corpus 11 (sigma 9, chronicle 1, kusto 1) `DWORD (0x00000010)` `DWORD (0x00000020)` `DWORD (0x00000030)`
`TargetObject`	ends_with	`\NtlmMinClientSec` `\RestrictSendingNTLMTraffic` `\lmcompatibilitylevel`
`TargetObject`	match	`ControlSet` corpus 3 (sigma 3) `SYSTEM\` corpus 2 (sigma 2) `\Control\Lsa`

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`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)

NetNTLM Downgrade Attack - Registry

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_regkey`

Stage 2: `selection_value_lmcompatibilitylevel`

Stage 3: `selection_value_ntlmminclientsec`

Stage 4: `selection_value_restrictsendingntlmtraffic`

Indicators

Keyboard shortcuts

Search operators

NetNTLM Downgrade Attack - Registry

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_regkey

Stage 2: selection_value_lmcompatibilitylevel

Stage 3: selection_value_ntlmminclientsec

Stage 4: selection_value_restrictsendingntlmtraffic

Indicators

Stage 0: `condition`

Stage 1: `selection_regkey`

Stage 2: `selection_value_lmcompatibilitylevel`

Stage 3: `selection_value_ntlmminclientsec`

Stage 4: `selection_value_restrictsendingntlmtraffic`