Techniques
Sample rules
GCP Unusual Number of Failed Authentications From Ip
- source: splunk
- technicques:
- T1586
- T1586.003
- T1110
- T1110.003
- T1110.004
Description
The following analytic identifies a single source IP failing to authenticate into Google Workspace with multiple valid users, potentially indicating a Password Spraying attack. It uses Google Workspace login failure events and calculates the standard deviation for source IPs, applying the 3-sigma rule to detect unusual failed authentication attempts. This activity is significant as it may signal an adversary attempting to gain initial access or elevate privileges. If confirmed malicious, this could lead to unauthorized access, data breaches, or further exploitation within the environment.
Detection logic
`gws_reports_login` event.type = login event.name = login_failure
| bucket span=5m _time
| stats dc(user_name) AS unique_accounts values(user_name) as tried_accounts values(authentication_method) AS authentication_method by _time, src
| eventstats avg(unique_accounts) as ip_avg , stdev(unique_accounts) as ip_std by _time
| eval upperBound=(ip_avg+ip_std*3)
| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0)
| where isOutlier =1
| `gcp_unusual_number_of_failed_authentications_from_ip_filter`