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Description

This analytic detects potential distributed password spraying attacks within an Office 365 environment. It identifies a significant increase in failed authentication attempts characterized by diverse user-and-IP address combinations, originating from multiple source IP addresses, and utilizing various user agents. These patterns may indicate an adversary's attempt to circumvent security controls by employing a spectrum of IP addresses to test commonly used passwords against a wide range of user accounts. The detection examines UserLoginFailed events from O365 Management Activity logs, with a particular focus on events with ErrorNumber 50126, which indicates a failed authentication due to incorrect credentials. By aggregating data over a five-minute interval, the analytic calculates the distinct counts of user-and-IP combinations and unique users and source IPs. It then applies a set of thresholds to these metrics to identify abnormal activities that could suggest a coordinated attack. The predefined thresholds within the analytic (such as unique IPs, unique users, etc.) serve as initial benchmarks and should be tailored to align with the organization's typical user behavior and risk tolerance. Early detection of such distributed activities is crucial for security operations centers (SOCs) to intercept unauthorized access attempts, avert account takeovers, and reduce the risk of subsequent malevolent actions within the organization's systems. A true positive alert from this analytic would indicate an ongoing distributed password spraying campaign targeting the organization's Office 365 tenant. If such an attack is successful, it could lead to unauthorized access, especially to accounts with administrative privileges, resulting in data breaches, privilege escalation, persistent threats, and lateral movement within the organization's digital environment.

  • Type: Hunting

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2023-11-09
  • Author: Mauricio Velazco, Splunk
  • ID: ea4e2c41-dbfb-4f5f-a7b6-9ac1b7f104aa

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1586 Compromise Accounts Resource Development
T1586.003 Cloud Accounts Resource Development
T1110 Brute Force Credential Access
T1110.003 Password Spraying Credential Access
T1110.004 Credential Stuffing Credential Access
Kill Chain Phase
  • Weaponization
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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 `o365_management_activity` Workload=AzureActiveDirectory Operation=UserLoginFailed ErrorNumber=50126 
| bucket span=5m _time 
| eval uniqueIPUserCombo = src_ip . "-" . user 
| stats dc(uniqueIPUserCombo) as uniqueIpUserCombinations, dc(user) as uniqueUsers, dc(src_ip) as uniqueIPs, values(user) as user, values(src_ip) as ips, values(user_agent) as user_agents by _time 
| where uniqueIpUserCombinations > 20 AND uniqueUsers > 20 AND uniqueIPs > 20 
| `o365_multi_source_failed_authentications_spike_filter`

Macros

The SPL above uses the following Macros:

:information_source: o365_multi-source_failed_authentications_spike_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
  • Workload
  • Operation
  • ErrorNumber
  • user
  • src_ip
  • user_agent

How To Implement

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events. The thresholds set within the analytic (such as unique IPs, unique users, etc.) are initial guidelines and should be customized based on the organization's user behavior and risk profile. Security teams are encouraged to adjust these thresholds to optimize the balance between detecting genuine threats and minimizing false positives, ensuring the detection is tailored to their specific environment.

Known False Positives

This detection may yield false positives in scenarios where legitimate bulk sign-in activities occur, such as during company-wide system updates or when users are accessing resources from varying locations in a short time frame, such as in the case of VPNs or cloud services that rotate IP addresses. Filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
42.0 70 60 An anomalous multi source authentication spike ocurred at $_time$

: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

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