Sigma rule: NetNTLM Downgrade Attack - Registry

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-017c2cbc6a9f, updated 2024-12-03T00:00:00.000Z.

Rule

Title
NetNTLM Downgrade Attack - Registry
Status
test
Level
high
Author
Florian Roth (Nextron Systems), wagga, Nasreddine Bencherchali (Splunk STRT)
Date
2018-03-20
Modified
2024-12-03
File
rules/windows/registry/registry_event/registry_event_net_ntlm_downgrade.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects NetNTLM downgrade attack

Log source

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_*

False positives (as the rule lists them)

  • Services or tools that set the values to more restrictive values

Tags

  • attack.persistence
  • attack.defense-impairment
  • attack.t1685
  • attack.t1112

MITRE ATT&CK ids this rule names

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/registry/registry_event/registry_event_net_ntlm_downgrade.yml

Sources and licences

  • SigmaHQ

    "NetNTLM Downgrade Attack - Registry" by Florian Roth (Nextron Systems), wagga, Nasreddine Bencherchali (Splunk STRT) (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/registry/registry_event/registry_event_net_ntlm_downgrade.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: NetNTLM Downgrade Attack - Registry",
entity page, dataset version ref-017c2cbc6a9f, updated 2024-12-03T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/d67572a0-e2ec-45d6-b8db-c100d14b8ef2 (accessed 2026-11-03).
Underlying source: SigmaHQ rule d67572a0-e2ec-45d6-b8db-c100d14b8ef2, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.