Office365: Brute Force Logon Success

Rule ID

PH_RULE_O365_BruteForceLogonSuccess

Default Status

Enabled

Description

Office365 Analytics Reported Brute Force Logon Attempts, including attempts that were seen as successful from the same source during the same period.

Severity

MITRE ATT&CK® Tactics

Credential Access

Credential Access consists of techniques for stealing credentials like account names and passwords. Techniques used to get credentials include keylogging or credential dumping. Using legitimate credentials can give adversaries access to systems, make them harder to detect, and provide the opportunity to create more accounts to help achieve their goals.

https://attack.mitre.org/tactics/TA0006

MITRE ATT&CK® Techniques

T1110.003

Brute Force: Password Spraying

Adversaries may use a single or small list of commonly used passwords against many different accounts to attempt to acquire valid account credentials.

https://attack.mitre.org/techniques/T1110/003

Impacts

Application

Data Source

Office 365 via Management Activity API

Detection

Correlation

Remediation Guidance

Identify the source of the incident and the user and make sure that it is a legitimate attempt to log on to the system. Make sure it is not a cached credential from another system while the primary user has changed credential. Make sure there are no other incidents from the source host that may indicate malware trying to gain access to other systems. Make sure there are no vulnerabilities on the source and destination hosts.

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

brute_force

SubPattern Definitions

SubPattern Name: brute_force

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType = "MS_OFFICE365_o365_brute_force"

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

srcIpAddr

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 srcIpAddr=brute_force.srcIpAddr

FortiSIEM Rules