MaxMpxCt Registry Value Changed

Severity: low
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

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.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1070.005` Indicator Removal: Network Share Connection Removal

Event coverage

Provider	Event ID	Title
Sysmon	13	RegistryEvent (Value Set)

Stages and Predicates

Stage 1: `selection`

TargetObject|endswith: '\Services\LanmanServer\Parameters\MaxMpxCt'

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.