Azure AD Unusual Number of Failed Authentications From Ip
Description
The following analytic identifies one source Ip failing to authenticate with multiple valid users. This behavior could represent an adversary performing a Password Spraying attack against an Azure Active Directory tenant to obtain initial access or elevate privileges. Error Code 50126 represents an invalid password.
The detection calculates the standard deviation for source Ip and leverages the 3-sigma statistical rule to identify an unusual number of failed authentication attempts. To customize this analytic, users can try different combinations of the bucket
span time and the calculation of the upperBound
field. This logic can be used for real time security monitoring as well as threat hunting exercises.
While looking for anomalies using statistical methods like the standard deviation can have benefits, we also recommend using threshold-based detections to complement coverage. A similar analytic following the threshold model is Azure AD Multiple Users Failing To Authenticate From Ip
.
- Type: Anomaly
-
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-07-11
- Author: Mauricio Velazco, Gowthamaraj Rajendran, Splunk
- ID: 3d8d3a36-93b8-42d7-8d91-c5f24cec223d
Annotations
ATT&CK
Kill Chain Phase
- Weaponization
- Exploitation
NIST
- DE.AE
CIS20
- CIS 10
CVE
Search
1
2
3
4
5
6
7
8
9
`azuread` category=SignInLogs properties.status.errorCode=50126 properties.authenticationDetails{}.succeeded=false
| rename properties.* as *
| bucket span=5m _time
| stats dc(userPrincipalName) AS unique_accounts values(userPrincipalName) as userPrincipalName by _time, ipAddress
| eventstats avg(unique_accounts) as ip_avg, stdev(unique_accounts) as ip_std by ipAddress
| eval upperBound=(ip_avg+ip_std*3)
| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1,0)
| where isOutlier = 1
| `azure_ad_unusual_number_of_failed_authentications_from_ip_filter`
Macros
The SPL above uses the following Macros:
azure_ad_unusual_number_of_failed_authentications_from_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
- properties.status.errorCode
- category
- properties.authenticationDetails
- properties.userPrincipalName
- properties.ipAddress
How To Implement
You must install the latest version of Splunk Add-on for Microsoft Cloud Services from Splunkbase (https://splunkbase.splunk.com/app/3110/#/details). You must be ingesting Azure Active Directory events into your Splunk environment through an EventHub. Specifically, this analytic leverages the SignInLogs log category.
Known False Positives
A source Ip failing to authenticate with multiple users is not a common for legitimate behavior.
Associated Analytic Story
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
54.0 | 60 | 90 | Possible Password Spraying attack against Azure AD from source ip $ipAddress$ |
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
- https://attack.mitre.org/techniques/T1110/003/
- https://docs.microsoft.com/en-us/security/compass/incident-response-playbook-password-spray
- https://www.cisa.gov/uscert/ncas/alerts/aa21-008a
- https://docs.microsoft.com/azure/active-directory/reports-monitoring/reference-sign-ins-error-codes
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: 2