SMB Create Remote File Admin Share

Severity: high
Author: Jose Rodriguez (@Cyb3rPandaH), OTR (Open Threat Research)
Source: upstream

Look for non-system accounts SMB accessing a file with write (0x2) access mask via administrative share (i.e C$).

MITRE ATT&CK coverage

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

Event coverage

Provider	Event ID	Title
Security-Auditing	5145	A network share object was checked to see whether client can be granted desired access.

Stages and Predicates

Stage 1: `selection`

AccessMask: 0x2
ShareName|endswith: 'C$'

Stage 2: `not 1 of filter_main_subjectusername`

SubjectUserName|endswith: '$'

Stage 3: `not 1 of filter_optional_local_ip`

IpAddress: '::1'

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
`AccessMask`	eq	`0x2` corpus 2 (sigma 2)
`IpAddress`	eq	`::1` corpus 5 (sigma 5)
`ShareName`	ends_with	`C$`
`SubjectUserName`	ends_with	`$` corpus 18 (sigma 14, elastic 4)

Neighbors

Broader alternatives (more inclusive than this rule)

These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.

Transferring Files with Credential Data via Network Shares [sigma] (drops 2 filters this rule applies) (first-stage match only; downstream stages may differ)