Potential Machine Account Relay Attack via SMB

Author: Elastic
Source: upstream

Identifies potential relay attacks against a machine account by identifying network share access events coming from a remote source.ip but using the target server computer account. This may indicate a successful SMB relay attack.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1187` Forced Authentication, `T1557` Adversary-in-the-Middle, `T1557.001` Adversary-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay
Lateral Movement	`T1021` Remote Services, `T1021.002` Remote Services: SMB/Windows Admin Shares
Collection	`T1557` Adversary-in-the-Middle, `T1557.001` Adversary-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay

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: `eql:file`

not source.ip ends_with and not source.ip:"127.0.0.1" and not source.ip:"::" and not source.ip:"::1" and user.name:"*$" and winlog.computer_name starts_with

Exclusions

Top-level NOT(...) conjuncts — predicates this rule actively suppresses.

Stage	Field	Kind	Excluded values
1	`source.ip`	ends_with	(no value — null check)

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
`source.ip`	ne	`127.0.0.1` corpus 8 (elastic 8) `::` `::1` corpus 7 (elastic 7)
`user.name`	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] (cross-vendor) (drops 6 filters this rule applies) (first-stage match only; downstream stages may differ)