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Description

The following analytic identifies instances where new IP addresses are added to the trusted IPs list in Office 365, potentially allowing users from these IPs to bypass Multi-Factor Authentication (MFA) during login. It leverages O365 audit logs, specifically focusing on events related to the modification of trusted IP settings. This activity is significant because adding trusted IPs can weaken the security posture by bypassing MFA, which is a critical security control. If confirmed malicious, this could lead to unauthorized access, compromising sensitive information and systems. Immediate investigation is required to validate the legitimacy of the IP addition.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Authentication
  • Last Updated: 2024-05-15
  • Author: Bhavin Patel, Mauricio Velazco, Splunk
  • ID: c783dd98-c703-4252-9e8a-f19d9f66949e

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1562.007 Disable or Modify Cloud Firewall Defense Evasion
T1562 Impair Defenses Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`o365_management_activity` Operation="Set Company Information." ModifiedProperties{}.Name=StrongAuthenticationPolicy 
| rex max_match=100 field=ModifiedProperties{}.NewValue "(?<ip_addresses_new_added>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2})" 
| rex max_match=100 field=ModifiedProperties{}.OldValue "(?<ip_addresses_old>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2})" 
| eval ip_addresses_old=if(isnotnull(ip_addresses_old),ip_addresses_old,"0") 
| mvexpand ip_addresses_new_added 
| where isnull(mvfind(ip_addresses_old,ip_addresses_new_added)) 
|stats count min(_time) as firstTime max(_time) as lastTime values(ip_addresses_old) as ip_addresses_old by user ip_addresses_new_added Operation Workload vendor_account status user_id action 
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `o365_bypass_mfa_via_trusted_ip_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_bypass_mfa_via_trusted_ip_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • signature
  • ModifiedProperties{}.Name
  • ModifiedProperties{}.NewValue
  • ModifiedProperties{}.OldValue
  • user
  • vendor_account
  • status
  • user_id
  • action

How To Implement

You must install Splunk Microsoft Office 365 add-on. This search works with o365:management:activity

Known False Positives

Unless it is a special case, it is uncommon to continually update Trusted IPs to MFA configuration.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 User $user_id$ has added new IP addresses $ip_addresses_new_added$ to a list of trusted IPs to bypass MFA

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 4