MaxMpxCt Registry Value Changed
Detects changes to the "MaxMpxCt" registry value. MaxMpxCt specifies the maximum outstanding network requests for the server per client, which is used when negotiating a Server Message Block (SMB) connection with a…
Description
Detects changes to the "MaxMpxCt" registry value. MaxMpxCt specifies the maximum outstanding network requests for the server per client, which is used when negotiating a Server Message Block (SMB) connection with a client. Note if the value is set beyond 125 older Windows 9x clients will fail to negotiate. Ransomware threat actors and operators (specifically BlackCat) were seen increasing this value in order to handle a higher volume of traffic.
Detection logic
Detection requirements
- Platform
- Windows
The rule states no platform. This is derived from the ATT&CK technique it maps to.
- Log source product
- windows
- Log source category
- registry_set
Known benign triggers
- Unknown
MITRE ATT&CK mappings
0 exclusive techniques.This is coverage no other published rule has; it is not this rule's total technique count.
References
| Reference | Cited by |
|---|---|
| securityscorecard.com/research/deep-dive-into-alphv-blackcat-ransomware | Only this detection cites it |
| www.huntress.com/blog/blackcat-ransomware-affiliate-ttps | Only this detection cites it |
| www.intrinsec.com/alphv-ransomware-gang-analysis/?cn-reloaded=1 | Only this detection cites it |
| www.sentinelone.com/labs/blackcat-ransomware-highly-configurable-rust-driven-raas-on-the-prowl-for-victims/ | Only this detection cites it |
From the source
- At source
- Open at source
- Upstream identifier
- 0e6a9e62-627e-496c-aef5-bfa39da29b5e
- Tagged by the source as
- attack.stealth
Licence
- Published under
- Detection Rule License 1.1Read the licence
- Attribution
- Required
Authorship
- Published
- Aug 26, 2026
- Version
- 1